Add retry logic when delete a nfs share using EMC VNX driver

[Peter Wang]

Currently, if user try to delete several nfs shares on same VDM,

vnx backend would report:
unable to acquire lock(s)

in this scenario, only 1 nfs share will be deleted, and other shares will be in error_deleting status

this fix is to provide a retry logic when meet this backend error

Thanks
Peter

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/208846

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/208846
Committed: https://git.openstack.org/cgit/openstack/manila/commit/?id=8d15b99022a32137035a24dad12ef74f3f145f41
Submitter: Jenkins
Branch: master

commit 8d15b99022a32137035a24dad12ef74f3f145f41
Author: peter_wang <email address hidden>
Date: Mon Aug 3 21:07:34 2015 -0400

    Add retry logic when delete a NFS share in VNX

    Currently, if user try to delete several NFS shares on same VDM,

    VNX backend would report: unable to acquire lock(s).

    Use 'retry' logic to handle such kind of error.

    Change-Id: I0dafbda265daf19de3d71ee91fc51fb62313e5ec
    Closes-Bug: 1480856