Fix vnf-topology-assign async

Updated vnf-topology-operation and vf-module-topolopy-operation
not to call assign-async directly.
Updated vnf-topology-operation-async and vf-module-topology-operation-async
to call assign-async instead of assign.

Change-Id: I16900ecb2126d2fe7fc3e1dfea351345272c275f
Issue-ID: SDNC-961
Signed-off-by: Timoney, Dan (dt5972) <dtimoney@att.com>