Update psrp and libpsl reference to Microsoft.PowerShell.Native
Keep the reference to powershell.myget.org in nuget.config for PSDesiredStateConfiguration and PowerShellHelpFiles
Update hosting tests
Update hosting.tests.csproj in preparation on next release with version 6.1.0-rc.1
Update Microsoft.Management.Infrastructure to version 1.0.0
* add csproj ref to sln
* Remove Microsoft.NET.Test.Sdk NuGet reference. The xunit.runner.visualstudio package is now sufficient for running tests in VS in the latest version (15.7.5)
* use RTM versions of XUnit 2.4.0 that got published today
* Update XUnit in hosting project as well to newer release