nuget.exe list command against v3 package source show friendly message when the v3 index.json does
not have an entry for 'LegacyGallery/2.0.0'
Added more tests for nuget.exe list to handle the following
1) v3 package source without an entry for package publish endpoint
2) v3 package source which is not available
Fixed with NuGetArchive/NuGet.PackageManagement#86