Need to get the path to the `dotnet.exe` host in GetRunInformation MSBuild target

[eerhardt]

We are currently returning dotnet.exe without a path in <Target Name="GenerateRunInformation"> in the Microsoft.DotNet.Core.Sdk.targets file.

We should either:

1. Figure out a way to get to the correct dotnet.exe to call from inside our MSBuild target.
2. Or pass back some sort of indicator to dotnet run that this project should use its host to run the project.

[brthor]

My 0.02c here.

For .NET Core MSBuild, it should use the path to the host it was invoked with. I think the closest we can currently get to this is resolving the path relative to the current shared framework deps file like here:

https://github.com/dotnet/cli/blob/rel/1.0.0/src/Microsoft.DotNet.Cli.Utils/Muxer.cs#L45

[eerhardt]

For .NET Core MSBuild, it should use the path to the host it was invoked with.

One concern is when MSBuild is running on the desktop framework, but building a .NET Core App. Say, for example, when invoked from VS.