Neutron makes call to nova for sending notifications but here no
context object user/admin available, so generated a request_id
and passed it as global_request_id during novaclient initialization
so that nova will log both global_request_id and it's own generated
request_id in the context formatter for traceability. As Notifier
class is used as singleton mode, need to create novaclient every time
events are sent from neutron to nova.
Modified unit tests wherever applicable.
Oslo spec I65de8261746b25d45e105394f4eeb95b9cb3bd42
Change-Id: I94257bd6ec9ec6b9a1f509c27c439e6305e43e63