Remove decorators for exceptions

Decorators for expected exceptions in comomn/rpc are handled by
allowed_rpc_exception_modules config option and should not be needed
in engine.py

Change-Id: I44cad13c1f717a12db6eca6bb7ccad312ce306be
blueprint: oslo-messaging
Refactor stack watching into a separate class

In later oslo.messaging patches, the Stack watch functionality must
be called from two separate places (the endpoint class and the service
class).  In order to do that and not result in needless code
duplication, break it into a separate class and so the object can
be passed around.

Change-Id: I4f4fae0182779d955ac0e15109fc641b271ddc01
blueprint: oslo-messaging
Merge "Remove decorators for exceptions"
Merge "Refactor stack watching into a separate class"