ComposeCache tests should target netcoreapp2.0

[eerhardt]

All of our ComposeCache tests all use netcoreapp1.0, but that TFM isn't supported by the cache feature, since the 1.x host doesn't know how to load assemblies from the cache.

We should move all our tests to test the product like our customers are going to use it, which means targeting netcoreapp2.0.

[ramarag]

Also ensure end to end feature runs properly by removing the TODOS in :

sdk/test/Microsoft.NET.Publish.Tests/GivenThatWeWantToPublishAProjectWithDependencies.cs

Line 153 in 517b4d5

//TODO: Enable testing the run once dotnet host has the notion of looking up shared packages

sdk/test/Microsoft.NET.Publish.Tests/GivenThatWeWantToPublishAProjectWithDependencies.cs

Line 192 in 517b4d5

//TODO: Enable testing the run once dotnet host has the notion of looking up shared packages

[ramarag]

I have upgraded the store tests as part of #1297

Outstanding items

1. please follow up on Store fixes #1297 (comment)
2. Complete the TODOS in
   a.

   sdk/test/Microsoft.NET.Publish.Tests/GivenThatWeWantToPublishAProjectWithDependencies.cs

   Line 161 in 34537c9

   //TODO: Enable testing the run once dotnet host has the notion of looking up shared packages

   
   b.

   sdk/test/Microsoft.NET.Publish.Tests/GivenThatWeWantToPublishAProjectWithDependencies.cs

   Line 200 in 34537c9

   //TODO: Enable testing the run once dotnet host has the notion of looking up shared packages

[eerhardt]

This work is now complete with #1363.