Fix bug where shuffleVirtualHostNameMap isn't updated

shuffleVirtualHostNameMap and shuffledSecureVirtualHostNameMap were
not being updated when the last instance was removed from an application.

Added unit test to illustrate the issue and fixed it by clearing the map
on every update, just as virtualHostNameAppMap gets cleared.
Merge pull request #240 from Knewton/fix-shuffleVirtualHostNameMap

Fix bug where shuffleVirtualHostNameMap isn't updated