Remove rescue/unrescue NotImplementedError handle

There are 2 kinds of RPC call from API layer to compute layer,
one is cast and another is call. For cast, the RPC message will
be posted and the API service will not wait for the message to
be processed. So it won't be able to catch the exception raised
in compute layer and catch and handle the exception is useless
and error leading. This patch removes code in API layer for
rescue and unrescue functions.

Change-Id: Iab8070c25a9dee505c0602efad85c41c21c2aa58
Merge "Remove rescue/unrescue NotImplementedError handle"