Add Microsoft.Extensions.DependencyModel dependency to test host nuspec

[smadala]

Fixes #393.
Should be merged after xUnit PlatformAbstraction fix release because DependencyModel 1.1 will break xUnit with error
System.IO.FileNotFoundException: Could not load file or assembly 'Microsoft.DotNet.InternalAbstractions, Version=1.0.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60.

Related issues: xunit/xunit#1080, xunit/xunit#1088

/cc @srivatsn @sbaid

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[smadala]

@onovotny Can you please provide tentative date for visualstudio.xunit 2.2-beta6 release?

[codito]

We need to take this for rtw.

@Faizan2304 this change requires the following as well?

• CrossPlatEngine refers DependencyModel 1.1.0 in 15.0-rtm branch
• Dotnet-CLI repo builds with DependencyModel 1.1.0

/cc @livarcocc

[davidfowl]

Is this already fixed? When is it going in?

[clairernovotny]

@davidfowl xunit beta6/RC has this fix already. The latest MyGet feed has it. I believe @bradwilson is publishing a quick RC any day now followed by the stable 2.2 ver.

[Faizan2304]

@Faizan2304 this change requires the following as well?
CrossPlatEngine refers DependencyModel 1.1.0 in 15.0-rtm branch
Dotnet-CLI repo builds with DependencyModel 1.1.0

Yes we should but some how its working without second point Dotnet-CLI repo builds with DependencyModel 1.1.0