ovs_lib should have a function to find br_name from datapath-id

[YAMAMOTO Takashi]

it's better to have a function to find br_name for the given datapath-id.

background:
i want the functionality for https://blueprints.launchpad.net/neutron/+spec/ofagent-bridge-setup .
i can just implement it in ofagent. however, ovs_lib is a better place as it can be possibly useful for other users of ovs.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/134440

[OpenStack Infra (hudson-openstack)]

Change abandoned by Kyle Mestery (<email address hidden>) on branch: master
Review: https://review.openstack.org/134440
Reason: This review is > 4 weeks without comment, and failed Jenkins the last time it was checked. We are abandoning this for now. Feel free to reactivate the review by pressing the restore button and leaving a 'recheck' comment to get fresh test results.

[Armando Migliaccio (armando-migliaccio)]

This bug is > 365 days without activity. We are unsetting assignee and milestone and setting status to Incomplete in order to allow its expiry in 60 days.

If the bug is still valid, then update the bug status.

[Launchpad Janitor (janitor)]

[Expired for neutron because there has been no activity for 60 days.]