x86 Server functional tests fail locally

The ServerComparison.FunctionalTests x86 tests fail if run directly because they look for the x86 runtime in the wrong place. It was recently moved from `%userprofile%\.dotnet\x86` to `%reporoot%\.dotnet\x86`

```
Failed ServerComparison.FunctionalTests.HelloWorldTests.HelloWorld(variant: Server: Kestrel, TFM: netcoreapp3.0, Type: Portable, Arch: x86)
Error Message:
System.Exception : Command exited unexpectedly with exit code: -2147450730
Stack Trace:
at Microsoft.AspNetCore.Testing.TaskExtensions.TimeoutAfter[T](Task`1 task, TimeSpan timeout, String filePath, Int32 lineNumber)
at Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer.StartSelfHostAsync(Uri hintUrl) in d:\github\AspNetCore\src\Hosting\Server.IntegrationTesting\src\Deployers\SelfHostDeployer.cs:line 190
at Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer.DeployAsync() in d:\github\AspNetCore\src\Hosting\Server.IntegrationTesting\src\Deployers\SelfHostDeployer.cs:line 65
at ServerComparison.FunctionalTests.HelloWorldTests.HelloWorld(TestVariant variant) in d:\github\AspNetCore\src\Servers\test\FunctionalTests\HelloWorldTest.cs:line 52
--- End of stack trace from previous location where exception was thrown ---
Standard Output Messages:
| [0.005s] TestLifetime Information: Starting test HelloWorld-Server: Kestrel, TFM: netcoreapp3.0, Type: Portable, Arch: x86 at 2019-02-21T19:37:07
| [0.003s] TestLifetime Information: Starting test HelloWorld_Kestrel_netcoreapp3.0_x86_Portable at 2019-02-21T19:37:07
| [0.004s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Information: Deploying [Variation] :: ServerType=Kestrel, Runtime=CoreClr, Arch=x86, BaseUrlHint=, Publish=False
| [0.005s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Information: Executing C:\Users\chrross\.dotnet\x86\dotnet.exe d:\github\AspNetCore\src\Servers\testassets\ServerComparison.TestSites\bin\Debug\netcoreapp3.0\ServerComparison.TestSites.dll --urls http://127.0.0.1:0/ --server Microsoft.AspNetCore.Server.Kestrel
| [0.006s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Information: Removing environment variable ASPNETCORE_ENVIRONMENT
| [0.006s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Information: SET ASPNETCORE_DETAILEDERRORS=true
| [0.007s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Information: SET ASPNETCORE_CONTENTROOT=d:\github\AspNetCore\src\Servers\testassets\ServerComparison.TestSites
| [0.048s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Information: Started C:\Users\chrross\.dotnet\x86\dotnet.exe. Process Id : 18680
| [0.169s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Warning: C:\Users\chrross\.dotnet\x86\dotnet.exe stderr: It was not possible to find any compatible framework version
| [0.170s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Warning: C:\Users\chrross\.dotnet\x86\dotnet.exe stderr: The specified framework 'Microsoft.NETCore.App', version '3.0.0-preview3-27414-8' was not found.
| [0.170s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Warning: C:\Users\chrross\.dotnet\x86\dotnet.exe stderr: - Check application dependencies and target a framework version installed at:
| [0.171s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Warning: C:\Users\chrross\.dotnet\x86\dotnet.exe stderr: C:\Users\chrross\.dotnet\x86\
| [0.171s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Warning: C:\Users\chrross\.dotnet\x86\dotnet.exe stderr: - The .NET Core framework and SDK can be installed from:
| [0.171s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Warning: C:\Users\chrross\.dotnet\x86\dotnet.exe stderr: https://aka.ms/dotnet-download
| [0.171s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Warning: C:\Users\chrross\.dotnet\x86\dotnet.exe stderr: - The following versions are installed:
| [0.172s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Warning: C:\Users\chrross\.dotnet\x86\dotnet.exe stderr: 2.0.0 at [C:\Users\chrross\.dotnet\x86\shared\Microsoft.NETCore.App]
| [0.172s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Warning: C:\Users\chrross\.dotnet\x86\dotnet.exe stderr: 2.0.9 at [C:\Users\chrross\.dotnet\x86\shared\Microsoft.NETCore.App]
| [0.172s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Warning: C:\Users\chrross\.dotnet\x86\dotnet.exe stderr: 2.1.2 at [C:\Users\chrross\.dotnet\x86\shared\Microsoft.NETCore.App]
| [0.172s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Warning: C:\Users\chrross\.dotnet\x86\dotnet.exe stderr: 2.1.6 at [C:\Users\chrross\.dotnet\x86\shared\Microsoft.NETCore.App]
| [0.173s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Warning: C:\Users\chrross\.dotnet\x86\dotnet.exe stderr: 2.1.7 at [C:\Users\chrross\.dotnet\x86\shared\Microsoft.NETCore.App]
| [0.173s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Warning: C:\Users\chrross\.dotnet\x86\dotnet.exe stderr: 2.2.0 at [C:\Users\chrross\.dotnet\x86\shared\Microsoft.NETCore.App]
| [0.173s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Warning: C:\Users\chrross\.dotnet\x86\dotnet.exe stderr: 2.2.1 at [C:\Users\chrross\.dotnet\x86\shared\Microsoft.NETCore.App]
| [0.174s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Warning: C:\Users\chrross\.dotnet\x86\dotnet.exe stderr: 3.0.0-preview-27217-02 at [C:\Users\chrross\.dotnet\x86\shared\Microsoft.NETCore.App]
| [0.174s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Warning: C:\Users\chrross\.dotnet\x86\dotnet.exe stderr: 3.0.0-preview-27219-3 at [C:\Users\chrross\.dotnet\x86\shared\Microsoft.NETCore.App]
| [0.174s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Warning: C:\Users\chrross\.dotnet\x86\dotnet.exe stderr: 3.0.0-preview-27319-3 at [C:\Users\chrross\.dotnet\x86\shared\Microsoft.NETCore.App]
| [0.175s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Warning: C:\Users\chrross\.dotnet\x86\dotnet.exe stderr: 3.0.0-preview-27324-5 at [C:\Users\chrross\.dotnet\x86\shared\Microsoft.NETCore.App]
| [0.175s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Warning: C:\Users\chrross\.dotnet\x86\dotnet.exe stderr: - Installing .NET Core prerequisites might help resolve this problem:
| [0.175s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Warning: C:\Users\chrross\.dotnet\x86\dotnet.exe stderr: https://go.microsoft.com/fwlink/?linkid=798306
| [0.180s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Information: host process ID 18680 shut down
| [0.180s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Information: Host process shutting down.
| [0.181s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Warning: Host process already exited or never started successfully.
| [0.181s] Microsoft.AspNetCore.Server.IntegrationTesting.SelfHostDeployer Information: [Time]: Total time taken for this test variation '0.1767904' seconds
| [0.181s] TestLifetime Information: Finished test HelloWorld_Kestrel_netcoreapp3.0_x86_Portable in 0.1785128s
| [0.190s] TestLifetime Information: Finished test HelloWorld-Server: Kestrel, TFM: netcoreapp3.0, Type: Portable, Arch: x86 in 0.18489519999999998s
```

The discovery logic is outdated:
https://github.com/aspnet/AspNetCore/blob/4451a804477f7f3d4d0ed89d56c51332d8c3ee25/src/Hosting/Server.IntegrationTesting/src/Deployers/ApplicationDeployer.cs#L108-L114
https://github.com/aspnet/AspNetCore/blob/4451a804477f7f3d4d0ed89d56c51332d8c3ee25/src/Hosting/Server.IntegrationTesting/src/Common/DotNetCommands.cs#L14-L21
@natemcmaster does this work from a full build because DOTNET_HOME gets set?