Comment 1 for bug 1407801

Rich Curran has committed a fix for this:

commit 8c01b26e770ff2c393ce7b9b92cac7cc05c4533e
Author: Rich Curran <email address hidden>
Date: Thu Jan 22 12:18:58 2015 -0500

    Single threading required for ML2 cisco/nexus driver

    During multi-VM creation (creates neutron ports) debug indicates that
    multiple threads are used in calls to the update and delete (on removing
    the VMs) methods. Since database access is used in the cisco nexus MD
    event methods for determining the current switch configuration, failures
    are seen (on both updates and deletes) on programming the nexus switch.

    This commit forces single threaded access to these methods.

    Change-Id: I275d1a8e43d69c2218b87f80283d325456d8948a