Make the Proprietary Test Resources portable

[amcasey]

I have a portable project with this project.json:

{
  "supports": {
    "net46.app": {}
  },
  "dependencies": {
    "Microsoft.CodeAnalysis.CSharp": "1.1.1",
    "Microsoft.NETCore": "5.0.0",
    "Microsoft.NETCore.Platforms": "1.0.0",
    "Microsoft.NETCore.Portable.Compatibility": "1.0.0",
    "Microsoft.NETCore.Targets": "1.0.0",
    "xunit": "2.1.0",
    "xunit.runner.console": "2.1.0"
  },
  "frameworks": {
    "dotnet": {
      "imports": "portable-net452"
    }
  }
}

When I try to add a nuget reference to the proprietary test resources, I get Microsoft.CodeAnalysis.Test.Resources.Proprietary 1.1.0-beta1-20150824-02 is not compatible with .NETPlatform,Version=v5.0.

Also, the proprietary test resources haven't been converted to use project.json and TestUtilities.csproj references them as a binary, rather than via nuget.

[amcasey]

FYI @agocke

[gafter]

@agocke @jaredpar What is the next step for this issue? What milestone should we assign it to?