No way to prioritize SDK resolvers error messages

With multiple SDK resolvers installed, when an SDK cannot be found, errors from _all_ the resolvers are displayed, whether they are useful or not.

For example:

```
/Users/mikayla/code/ProjectFae/Source/ProjectFaeMono/ProjectFaeMono.csproj : error : /usr/local/share/dotnet/sdk/2.1.4/Sdks/Mono.UE4.Sdk/Sdk not found. Check that a recent enough .NET Core SDK is installed and/or increase the version specified in global.json.
/Users/mikayla/code/ProjectFae/Source/ProjectFaeMono/ProjectFaeMono.csproj : error : Could not find UE4 engine matching '{15B0F9D0-4216-D682-DA95-EC969882E53B}'
Project "/Users/mikayla/code/ProjectFae/ProjectFae_Managed.sln" (1) is building "/Users/mikayla/code/ProjectFae/Source/ProjectFaeMono/ProjectFaeMono.csproj" (2) on node 1 (default targets).
/Users/mikayla/code/ProjectFae/Source/ProjectFaeMono/ProjectFaeMono.csproj : error MSB4236: The SDK 'Mono.UE4.Sdk' specified could not be found.
```

In this case, the error `Could not find UE4 engine matching '{15B0F9D0-4216-D682-DA95-EC969882E53B}'` provides useful information to help fix the error, as it comes from a resolver that knows how to handle the Mono.UE4.Sdk SDK. The error from the .NET Core resolver is irrelevant, and the final error doesn't add much useful information.