The VS SDK team provided us with an updated NuGet that has better error
diagnostics during install / uninstall.  Going to change our VSI tests
to begin using build based deployment again for VSIX until they can get
the diagnostics that they need.  Once they have them will flip it back.

This was reverted as a part of 5fe4adb3 but should have been
put back.

Create the Packages.props and FixedPackages.props.  These are the files
which will contain our MSBuild mapping from packag name to package
version