[master] Update dependencies from dotnet/arcade dotnet/core-setup dotnet/corefx (#17458)
* Update dependencies from https://github.com/dotnet/arcade build
20191018.2
- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.19518.2
- Microsoft.DotNet.Helix.Sdk - 5.0.0-beta.19518.2
* Update dependencies from https://github.com/dotnet/core-setup build
20191021.2
- Microsoft.NETCore.App - 5.0.0-alpha1.19521.2
* Update dependencies from https://github.com/dotnet/corefx build
20191020.7
- Microsoft.Private.CoreFx.NETCoreApp - 5.0.0-alpha1.19520.7
* Update dependencies from https://github.com/dotnet/arcade build
20191023.3
- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.19523.3
- Microsoft.DotNet.Helix.Sdk - 5.0.0-beta.19523.3
* Update dependencies from https://github.com/dotnet/core-setup build
20191023.10
- Microsoft.NETCore.App - 5.0.0-alpha1.19523.10
* Update dependencies from https://github.com/dotnet/corefx build
20191023.8
- Microsoft.Private.CoreFx.NETCoreApp - 5.0.0-alpha1.19523.8
* Disable a file system watcher test on mac
See https://github.com/mono/mono/issues/17547
* Reenable tests that were fixed