Remove code no longer needed now that stable/queens is the oldest
supported branch, and enhance compatabilty with newer neutron
branches. Highlights include:
* Use definitions from neutron_lib where appropriate.
* Add gbpservice.neutron.db.api wrapper for definitions in
neutron_lib.db.api in stable/rocky and newer that aren't moved yet
in stable/queens, so that most DB code can remain unchanged across
branches. In particular, this replaces db_api.context_manager.reader
with db_api.CONTEXT_READER and db_api.context_manager.writer with
db_api.CONTEXT_WRITER.
* Eliminate some DeprecationWarning messages, such as those due to
'tenant' being renamed 'project'.
* [AIM] Remove validation tool support for migrating SNAT resources
from the legacy ACI plugin.
* [AIM] Fix make_port_context to use a CONTEXT_WRITER instead of a
CONTEXT_READER, since it can call get_network, which uses a
CONTEXT_WRITER and transactions cannot be upgraded from read-only to
read-write.
* [AIM] Change UTs to use make_port_context instead of
get_bound_port_context to prevent trying to bind the port if its not
already bound.
* [AIM] Remove quota-related monkey-patching that is no longer needed
due to previous technical debt cleanup.
* [AIM] Use the registry.receives decorator instead of calling
registry.subscribe.
* [AIM] Fix TypeError in _agent_bind_port.
* [AIM] Simplify _net_2_epg function in test_apic_aim UT module.
Change-Id: I01d57debd6884032267a6b7675883b6d1e61afcc
7f460160d6