Error list does not always contain all errors from the build output

**Repro Steps**

Create a 1.1 NET Core project (there are templates in VS for 1.1 web projects)
Add a unit test project - the default template in VS targets NetCore 1.0
Add a ref from the test project to the first one.
Build

It is not happening to me, but I've seen this in two different instances on @jinujoseph's machine.

https://github.com/dotnet/sdk/issues/798#issuecomment-277329066

Output Window:
```
1>------ Build started: Project: WebApplication1, Configuration: Debug Any CPU ------
1>WebApplication1 -> C:\Users\jinuj\documents\visual studio 2017\Projects\WebApplication1\WebApplication1\bin\Debug\netcoreapp1.1\WebApplication1.dll
2>------ Build started: Project: UnitTestProject2, Configuration: Debug Any CPU ------
2>C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\Sdks\Microsoft.NET.Sdk\build\Microsoft.NET.Sdk.Common.targets(69,5): error : Project 'C:\Users\jinuj\documents\visual studio 2017\Projects\WebApplication1\WebApplication1\WebApplication1.csproj' targets '.NETCoreApp,Version=v1.1'. It cannot be referenced by a project that targets '.NETCoreApp,Version=v1.0'.
2>Done building project "WebApplication1.csproj" -- FAILED.
2>C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\Sdks\Microsoft.NET.Sdk\build\Microsoft.NET.Sdk.targets(76,5): error : Cannot find project info for 'C:\Users\jinuj\documents\visual studio 2017\Projects\WebApplication1\WebApplication1\WebApplication1.csproj'. This can indicate a missing project reference.
2>Done building project "UnitTestProject2.csproj" -- FAILED.
========== Build: 1 succeeded or up-to-date, 1 failed, 0 skipped ==========
```

Error List:


@davkean @srivatsn This is especially bad because in both instances I've seen it, there were helpful messages in the output that are harder to read there and the error list picked up only secondary consequences of the root problem with undecipherable messges.