Kill 'Skipping unknown group key: firewall_driver' log trace

This is done by trying to import the option first. If this
does not work, emit a warning instead as in most cases this is
harmless for a number of reasons: a) the service might not
even need the opt; b) if things do break down the line, we'll
see bigger traces; c) it's not gonna be long for this legacy
quantum/neutron stuff to be removed altogether.

Closes-bug: 1210121

Change-Id: I34917da9cb6117ee1d42140621c742f503279b6b
(cherry picked from commit b5ee49623982530bfb3c3fe2eefb9d8ddb6353bc)
NVP plugin:fix delete sec group when backend is out of sync

If a security group does not exist on the NVP backend, an error
should not be raised on deletion of the security group.

This patch changes the plugin behavior by deleting the record
from the database and just logging that the security group
was not found on the NVP backend.

Closes-Bug: #1251422

Conflicts:
	neutron/tests/unit/nicira/test_nicira_plugin.py

Change-Id: Ib8adf7a830ff336655fd83ad4118cde641adf284
(cherry picked from commit ed83265bb794d38f6f66d9e5182a9abc6b82ed53)
Merge "NVP plugin:fix delete sec group when backend is out of sync" into stable/havana
Merge "Kill 'Skipping unknown group key: firewall_driver' log trace" into stable/havana
Merge branch 'stable/havana' of https://github.com/openstack/quantum into havana/stable