Add L2 Agent side handling for non consistent security_group settings

Add setting of the firewall_driver to NoopDriver when firewall_driver is None and
add warning if driver combination is not valid.
Modify is_valid_driver_combination to verify default settings: enable_security_group (True) and firewall_driver (None).

Change-Id: I841f9cf96ac6ee2ad17a4e8908d6c8a96f368cca
Closes-Bug: #1296957
Enforce required config params for ODL driver

Raise a config error during initialization if
there is no URL, username, or password specified
in the config for the OpenDayLight ML2 driver.

Closes-Bug: #1301432
Change-Id: I65fc94d3eaaade3d1402d1c82d2c1edfa7133d5a
Merge "Enforce required config params for ODL driver"