VMR does not properly respect pre-set NUGET_PACKAGES paths

[mmitche]

if NUGET_PACKAGES is set when running build.sh/cmd the initial toolset restore will restore arcade to that directory, but then this variable will be unset, a different value will be chosen for NUGET_PACKAGES, and the first repo looking for that bootstrap arcade will fail to build.

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.