Migrations fail when dropping a non-existent index

[Mahesh Panchaksharaiah]

Migrations which modify indexes first drop the existing index before creating a new one. If the index is missing for some reason the migration fails.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/53318

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/53318
Committed: http://github.com/openstack/nova/commit/aadc7b89131f3d46070e7e5478156e3cf623dbe6
Submitter: Jenkins
Branch: master

commit aadc7b89131f3d46070e7e5478156e3cf623dbe6
Author: Mahesh Panchaksharaiah <email address hidden>
Date: Wed Oct 23 15:42:59 2013 +0530

    Checking existence of index before dropping

    Migrations modifying indexes drop and recreate the index.
    If an index does not exist dropping would fail the migration.
    As part of this fix, checking if index exists before dropping it.

    Fixes bug 1243553

    Change-Id: Ic75744bdccfbc516d36a9711ad6997fd86c7a722