LBaaS: Fix incorrect pool status change

Avoid incorrect status change when deleting the pool.
We can check for the conditions prior putting the pool
to PENDING_DELETE state, in case delete conditions are met
it is safe to change the state to PENDING_DELETE.
Also, change create_vip and update_vip operations to respect
PENDING_DELETE and avoid race conditions.

Change-Id: I9f526901eb85bdb83cf4ff8131460eb592c900f8
Closes-Bug: #1242338
Ensure OVS plugin is loaded in OVS plugin test

In TestOpenvswitchSGServerRpcCallBack and NetworkBindingsTest
in OVS plugin tests, OVS plugin was not loaded properly.

* For NetworkBindingsTest, it can be fixed by changing setUp()
  to take 'plugin' arguments in the base test classes
  SecurityGroupDBTestCase and SGServerRpcCallBackMixinTestCase.
  This fixes bug 1242510 in ML2 unit tests.

* For NetworkBindingsTest, it can be fixed by passing the plugin
  class to super.setUp(). The test itself needs to be updated
  because network binding is added when a network is created.

* NetworkBindingsTest in Linux Bridge plugin has the same issue,
  so it is also fixed in this patch.

Closes-Bug: #1230083
Closes-Bug: #1242510
Change-Id: I914876225480585d822748c188e9b69d1adf46f3
Merge "Ensure OVS plugin is loaded in OVS plugin test"
Merge "LBaaS: Fix incorrect pool status change"