Merge changes from TFS

[dotnet-bot]

No description provided.

[jkotas]

@dotnet-bot test OSX x64 Checked Build and Test please

[jkotas]

@dotnet-bot test Ubuntu x64 Checked Build and Test please

[jkotas]

The OSX failures are same tracked by #3755.

The Ubuntu failures are: System.IO.FileNotFoundException: Could not load file or assembly 'System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies.

System.Private.CoreLib is .NET Native / CoreRT assembly. It should not ever exist for CoreCLR. This error means that Nuget restored assemblies for CoreRT runtime, not for CoreCLR runtime. The failure persist even on reruns - the nuget cache on the Ubuntu machine may be corrupted.

@wtgodbe Is there a way to recycle the Ubuntu machine?

[wtgodbe]

@jkotas do you mean redo the ubuntu test? The only way to do that is to redo all 8 tests with "test this please"

[wtgodbe]

I'm not sure how to go about clearing the nuget cache on one of the CI machines - @mmitche might know

[sergiy-k]

The error has nothing to do with Nuget restore. CoreFX added AOT assemblies to the build together with CoreCLR assemblies and all of them ended up under the same bin folder (Linux.AnyCPU.Release). In addition, corefx changed/renamed versioning for AOT (netstandard13aot, netcore50aot, netstandard15aot) a few times during last week which broke the logic in runtests.sh for creating the CORE_OVERLAY folder.
I think that the last break was caused by dotnet/corefx@d37bcde#diff-129d51903b50de469a0a506e6847d1d0 which introduced netstandard15aot by renaming netstandard13aot=>netstandard15aot. I have submitted a PR to fix it (#3782).