Comment 6 for bug 1737131

Reviewed: https://review.opendev.org/660706
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=656aa1cd40570154df606484d31616989b5296aa
Submitter: Zuul
Branch: stable/stein

commit 656aa1cd40570154df606484d31616989b5296aa
Author: Silvan Kaiser <email address hidden>
Date: Wed Nov 22 14:35:11 2017 +0100

    Fixes multi-registry config in Quobyte driver

    This closes a bug concerning multi-registry configurations
    for Quobyte volumes due to no longer using the is_mounted()
    method that failed in that case.
    Besides, this adds exception handling for the unmount call that
    is issued on trying to mount an already mounted volume.

    NOTE: The original commit also added a new feature (fs type
    based validation) which is omitted in this backport.

    Closes-Bug: #1737131

    Change-Id: Ia5a23ce1123a68608ee2ec6f2ac5dca02da67c59
    (cherry picked from commit 05a73c0f3a9f8edf9024f9870279bc6fb7bba2e7)