Improve error handling in GPFS driver for remote execution

[Nilesh Bhosale]

IBM GPFS Manila driver when executing commands over SSH, does not check for exit codes from the commands executed remotely.
This needs to be improved and the error needs to be checked.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/159771

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/159771
Committed: https://git.openstack.org/cgit/openstack/manila/commit/?id=fe51a03874c2d3144d34b229c614b59eda2baf24
Submitter: Jenkins
Branch: master

commit fe51a03874c2d3144d34b229c614b59eda2baf24
Author: Nilesh Bhosale <email address hidden>
Date: Fri Feb 27 15:21:52 2015 +0530

    Improve error handling in GPFS driver

    Improving the error handling and error messages as follows:
    - Check for exit status for the commands executed over SSH
    - Following Log Translation guidelines

    Change-Id: Ide6a37d9c00062ce4b025063da97f2e236c4f986
    Closes-Bug: #1420739