Added a FeedOnlyMode configuration to allow service feeds only
Update ServiceConfiguration csdef as well
Always register the home route
// The home route is used as a probe path by Azure Load Balancer
// to determine if the node is up. So, always register the home route
// Just do so with an Empty Home, in the FeedOnlyMode, which simply returns a 200
Prevent user registration in FeedOnlyMode
Prevent user registration in FeedOnlyMode. Add FeedOnlyModeException.cs to csproj
Added a period at the end of error message
Refactored Route Registration methods.
There is always the RegisterRoutes method which the AppActivator and test
methods call with/without bool feedOnlyMode
Doing it the old way w.r.t RegisterServiceRoutes(). Call it independently
from the rest of the routes. Otherwise, a lot of unit tests fail
Merge pull request #2212 from NuGet/daravind/FeedOnlyMode

Added FeedOnlyMode to support NuGetV2RepositoryMirrors