Allow ports to be created on networks that do not exist in NVP

Allow ports to be created on networks that do not exist in NVP

If a network exists in the quantum database but not in NVP we should allow
someone to create a port on this network and set the status to ERROR. The
reason for this is if one deletes a network from NVP and when the dhcp agent
goes to create it's dhcp port on this network an error will be raised to the
agent and it will enter a constant state of resyncing.

This patch also adds a unit test for update_port() for the same situation.

Fixes bug 1179327

Change-Id: Ie77fc48d11644b820c0cc3b3fa341856e36f8511