Backup restore fails with ephemeral support enabled

[Steve Leon]

Creating an instance from a backup fails when using ephemeral storage (trove_volume_support = False).

When using ephemeral, nova automatically mounts the ephemeral drive /dev/vdb into /mnt. This causes issues during the restore from backup when the restore method tries to delete all files from the mounted device. It gets an error complaining about the "Device or resource busy".

This is the line where it fails:
https://github.com/openstack/trove/blob/master/trove/guestagent/strategies/restore/mysql_impl.py#L126

To solve the problem, we should unmount the ephemeral storage if it's been already mounted.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/81379

[Openstack Gerrit (openstack-gerrit)]

Reviewed: https://review.openstack.org/81379
Committed: https://git.openstack.org/cgit/openstack/trove/commit/?id=f173997da46be0ef9c93c2196af3447f5921d584
Submitter: Jenkins
Branch: master

commit f173997da46be0ef9c93c2196af3447f5921d584
Author: Steve Leon <email address hidden>
Date: Tue Mar 18 14:51:37 2014 -0700

    Unmounting ephemeral if it has already been mounted

    Creating an instance from a backup fails when using
    ephemeral storage (trove_volume_support = False).
    When using ephemeral, nova automatically mounts the ephemeral
    drive /dev/vdb into /mnt. This causes issues during the restore
    from backup when the restore method tries to delete all files from
    the mounted device. It gets an error complaining about the
    "Device or resource busy".

    To solve the problem, we should unmount the ephemeral storage
    if it's been already mounted.

    Change-Id: I007c1e11274f1f497d26bd9b1be1fc5b0830f84b
    Closes-Bug: #1294369