Update CoreFx build to shipping nuget

[ericstj]

Need to do the following to bring ourselves current with the shipping nuget scenarios.

• switch from DNX to nuget.exe
• move projects from dnxcore50 to netstandard1.x
• switch to stable version consumption of packages
• use PCL meta-package in all test projects
• eliminate test-runtime\project.json hack
• ensure we use inbox nuget task/targets when present and only use BuildTools version when inbox is missing

[mellinoe]

Just looking for some clarification, as someone who isn't as familiar with how everything is expected to work.

switch from DNX to nuget.exe

So presumably we will still be downloading NuGet.exe as we are today, but instead of using it to restore dnx/dnu, we will just use it to restore the rest of the packages? Sounds like a more straightforward process :)

move projects from dnxcore50 to dotnet with appropriate supports gaurdrails

What "guardrails" do we need and/or what are they for? I'm not familiar with this terminology.

use PCL meta-package in all test projects

Will this buy us anything other than reducing the number of dependencies we need to list? I'm not sure what all the PCL meta-package contains.

ensure we use inbox nuget task/targets when present and only use BuildTools version when inbox is missing

(Assuming "inbox" targets means "Visual Studio" targets)
Maybe I'm thinking about this the wrong way, but it makes more sense to me to just use a single set of build targets everywhere, rather than special-case machines with VS installed, given that we need to support cross-plat builds. It will probably just be added complexity if we have to consider two different sets of targets as well. I was hoping that we were moving away from dependencies on other products and getting to a place where all of the build dependencies could be downloaded or copied in as part of the regular build process.

Some of these are just regarding the terminology, which I'm not fully familiar with, so others may have similar questions.

[davidfowl]

move projects from dnxcore50 to dotnet with appropriate supports gaurdrails

I don't think so, this needs to be updated to use a specific platform standard.

use PCL meta-package in all test projects

Maybe? That'll all of the packages all the time. Which is insanity.

[ericstj]

Opened dotnet/buildtools#917 to track the ResolveNuGetPackageAssets task.
PCL meta-package for tests is a non-goal.