Enable PCM workflows in package reference scenarios

[drewgillies]

Repro Steps:

1. New a C# Console App (.Net Framwork).
2. Add the following properties to the property group at the top of the csproj file:
   <RuntimeIdentifiers Condition="'$(RuntimeIdentifiers)'==''">win</RuntimeIdentifiers>
3. Add the following reference to the csproj file, before the final targets import line starting with

<Import Project="$(MSBuild...
<ItemGroup> 
       <PackageReference Include="Newtonsoft.Json"> 
            <Version>6.0.1</Version> 
      </PackageReference> 
 </ItemGroup>

4. Reload the project in VS and run solution restore.
5. Open PM UI and install package ‘NUnit’ 3.0.0.
6. Click ‘Updates’ tabs and observe it.
7. Open PMC, type ‘update-package’ and press ‘Tab’ key.
8. Type ‘get-package -updates’ in PMC.
9. Type ‘Uninsall-Package’ and press ‘Tab’ key.

Expected:
Can find package update and uninstall package via the package manager UI and the package manager console.

Actual:
Can not uninstall and update package via the package manager UI and the package manager console.

[jainaashish]

Merged to Dev 17fe755 Waiting for RC2 decision

[rrelyea]

dupe of #4015