Add option to run performance tests using run_tests.sh

[Kamil Sambor]

We need separate option to make possible to run performance tests only.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/144322

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/144322
Committed: https://git.openstack.org/cgit/stackforge/fuel-web/commit/?id=30e4d4e65508e4c6872a3728ff27862df6249f47
Submitter: Jenkins
Branch: master

commit 30e4d4e65508e4c6872a3728ff27862df6249f47
Author: Julia Varigina <email address hidden>
Date: Mon Dec 29 08:17:37 2014 -0800

    Added an option to run Nailgun performance test

    A new option -x added

    run_tests.sh [-x | --performance]
                 - run nailgun performance tests

    If -x option is not specified, run_test.sh will not run
    performance tests. For this reason no matching -X option was added.

    Option -n | -N works exactly as before: run | do not run
    Nailgun non-performance tests.

    Examples of usage:
    run_tests.sh -n -x - run both regular and performance nailgun tests.
    run_tests.sh -x - run nailgun performance tests only, do not run
                         regular nailgun tests
    run_tests.sh -n - run regular nailgun tests only
    run_tests.sh -N - run all tests except for nailgun regular and
                         performance tests

    DocImpact
    Change-Id: Id155e722da88549499641f5b924f35bfab3ab137
    Closes-Bug: #1394196