Cisco plugin (grizzly) device connection errors

This commit fixes the Cisco plugin device connections issue where the plugin would drop
connections to the Nexus switches.

Change-Id: I9f09d22cb359b4fcdae5f5063a97011d82daf5a1
Fixes: Bug 1212834
Merge "Cisco plugin (grizzly) device connection errors" into stable/grizzly
Merge branch 'stable/grizzly' of https://github.com/openstack/quantum into grizzly/stable