Hooks add the ability to insert custom code around operations that
declare a named hook:
e.g.
@hooks.add_hooks('create_instance')
def create_instance(....):
....
The above hook allows Hook objects to be run 'pre' and 'post' the
execution of create_instance()
Hook objects are discovered via the setuptools entry point group
'nova.hooks'.
Change-Id: I3961df12ef415085de7459438967edacc34500c2
e937a53065