Make status decription field for cluster more useful

[Vitalii Gridnev]

We have only one place where status decription field is been setted. We can use this field to store some initial information about cluster failures

Why this changes are required:

1) We use status description field only during validating
cluster. We can use it for finding initial reasons of
cluster errors (for example, we have problems with launching
instances with nova). Other reasons of failures
we can find with event-log feature.
2) It doesn't require any another changes in REST API
and DB, because we already can get info about status
description from REST API

Also, it was added patch to Horizon, which allows to
view status_description for cluster from UI (see here:
https://review.openstack.org/#/c/154829/)

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/154014

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/154014
Committed: https://git.openstack.org/cgit/openstack/sahara/commit/?id=5b30113fcaa71ca87a0c67f17b5f176d95286f85
Submitter: Jenkins
Branch: master

commit 5b30113fcaa71ca87a0c67f17b5f176d95286f85
Author: Vitaly Gridnev <email address hidden>
Date: Mon Feb 9 15:39:09 2015 +0300

    Make status description field more useful

    If during operating cluster some error occurs, status
    description field for cluster will be updated with
    exception message

    Change-Id: I8973a4ac0d1dbab9c58787d385c12451eb67b1ef
    Closes-bug: #1419136