[OSTF] Need to refactor cloudvalidation test

[Alexander Gubanov]

1. We need to remove excess "cat" and "tail" commands in cloudvalidation/test_disk_space_db.py [1], because "grep" already has this functionality.
Also, we should use "fgrep" to disable mechanism of regular expression - on big search will complete faster.

2. "Ugly" output if test failed:

Free disk space cannot be used by database on node(s): [u'10.177.30.6', u'10.177.30.5'].
Please refer to OpenStack logs for more details.

[1]: https://github.com/stackforge/fuel-ostf/blob/master/fuel_health/tests/cloudvalidation/test_disk_space_db.py#L34-L35

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/237956

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/237956
Committed: https://git.openstack.org/cgit/openstack/fuel-ostf/commit/?id=9f500668555292add5d87c942e0cd804aefa6df2
Submitter: Jenkins
Branch: master

commit 9f500668555292add5d87c942e0cd804aefa6df2
Author: Tatyana Leontovich <email address hidden>
Date: Wed Oct 21 12:40:23 2015 +0300

    Replace cat usage for fgrep

    Replace "cat" command to "fgrep" in test test_disk_space_db

    Change-Id: Ia6bd197f3b7448df7834a3cc9384661c1eccc9df
    Closes-Bug: #1491294

[Alexander Gubanov (ogubanov)]

Patch doesn't fix all issues described above, I mean:
>2. "Ugly" output if test failed:

[Tatyanka (tatyana-leontovich)]

This tests disabled and is not executed - so it can be failed at all

[Tatyanka (tatyana-leontovich)]

So move to invalid

[Tatyanka (tatyana-leontovich)]

Test is disabled since 7.0 (https://github.com/openstack/fuel-ostf/blob/master/fuel_health/tests/cloudvalidation/test_disk_space_db.py#L53) So it is not discovered and is not appear.