Fix for bugs 446 and 456

Fix for "Null pointer exception on remove_router_interface" (Bug 446)
and "Return better error messages from NeutronAPIService" (Bug 456)

Change-Id: I60c24ac37a91653e4c6f5ff2d654e8f85ad78d44
Signed-off-by: Ryan Moats <rmoats@us.ibm.com>
Merge "Fix for bugs 446 and 456"