NSX: Sync do not pass around model object

The NSX sync backend previously passed around a sqlalchemy model object
around which was nice because we did not need to query the database an
additional time to update the status of an object.

Unfortunately, this was add done within a db transaction which included a
call to NSX which could cause deadlock this needed to be removed. Now a
dict is passed around instead and proper transaction handling
is used when updating objects.

Closes-bug: #1281772

Conflicts:
	neutron/plugins/nicira/common/sync.py

Change-Id: Id50abd8f2143b127d1ca81c360c1c6d400e1d74f
(cherry picked from commit 084b7f62280241a9037b6f9e592c466135e5fec1)
Merge "NSX: Sync do not pass around model object" into stable/havana