Add bulking support for Cisco plugin

Add bulking support for Cisco plugin

For each bulk request, the Cisco plugin will handle the call,
and, through the base class method, convert them into a series of
non-bulking calls wrapped in a transaction (emulated bulking).

Those non-bulking requests will all be forwarded to the Cisco
model (VirtualPhysicalSwitchModelV2), which will either handle
the request locally (as in create_port), or delegate the request
to the OVS plugin (OVSQuantumPluginV2).

As a result, the model should not receive any bulking calls.
However, the model was set up to delegate any bulk calls to the
OVS plugin (which would act like the existing code, in case we
decide later to pass along any bulk calls). An alternative would
be to raise an exception, if a bulk call was made to the model.

Prior to this change, all bulking calls were forwarded from the
Cisco plugin to the model plugin, which would would delegate
(directly or indirectly) to the OVS plugin. The OVS plugin would
turn the request into a transction of non-bulking calls.

The effective difference proposed is that the create_port will now
create the port in OVS and then create the network in the Nexus
plugin.

The Nexus plugin does not currently handle bulking so this commit
is implementing emulated (versus native) bulking.

This patch has been updated with latest from upstream (Havana).

blueprint bulk-api-cisco-plugin
Change-Id: I874295b32ea20c2ca393228b0893a9dd6c77baf2