Fix process attribute check in BackupRunner

[Petr Malik]

Base 'BackupRunner' checks for the 'process' attribute on __exit__
and terminates the runner process if any.
It however always initializes the process to 'None' in the __init__.
That check is therefore always True.
It should change the condition to check for 'None' value instead.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/177508

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/177508
Committed: https://git.openstack.org/cgit/openstack/trove/commit/?id=d68ecc03cba517b68910d5bda2b2ceb786b2fe35
Submitter: Jenkins
Branch: master

commit d68ecc03cba517b68910d5bda2b2ceb786b2fe35
Author: Petr Malik <email address hidden>
Date: Fri Apr 24 15:36:06 2015 -0400

    Fix process attribute check in BackupRunner

    Base 'BackupRunner' checks for the 'process' attribute on __exit__
    and terminates the runner process if any.
    It however always initializes the process to 'None' in the __init__.
    That check is therefore always True.
    It should change the condition to check for 'None' value instead.

    I also made the 'run' method 'protected' to keep it consistent with the
    'pre' and 'post' methods (and also the restore runner which
    has the process handling method protected as well).

    Change-Id: I6e98a47d33de7da95d884fb67b2cfab918183b3b
    Closes-Bug: 1448279