ML2 Cisco Nexus MD: Create pre/post DB event handlers

[Rich Curran]

Split ML2 cisco nexus event handers for update and delete into precommit (called during DB transactions) and postcommit (called after DB transactions) methods.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/56478

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/56478
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=8d0abf2db701803eaf11c0a8ff4d759b0da5dc39
Submitter: Jenkins
Branch: master

commit 8d0abf2db701803eaf11c0a8ff4d759b0da5dc39
Author: Rich Curran <email address hidden>
Date: Thu Nov 14 17:20:07 2013 -0500

    ML2 Cisco Nexus MD: Create pre/post DB event handlers

    Split ML2 cisco nexus event handers for update and delete
    into precommit (called during DB transactions) and postcommit
    (called after DB transactions) methods.

    Also fixes some unit tests that were incorrectly accessing
    context managers without using the "with" statement.

    Closes-Bug: #1241098
    Change-Id: I59b046342706230222c1be39d13a455ca5a884ea