Refactor tempest common

Refactor tempest common

It also renames two testcases and updates all docs because tests
run in parallel in case of tempest smoke.

To force one thread as before:
run:
    module: 'functest.opnfv_tests.openstack.tempest.tempest'
    class: 'TempestCommon'
    args:
        mode: '^tempest\.(api|scenario).*\[.*\bsmoke\b.*\]$'
        option:
            - '--concurrency=1'

JIRA: FUNCTEST-989

Change-Id: I1348f5908400a5046be8edf983db4afa12e546c3
Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>
(cherry picked from commit eb8f57466325f398c6b8b5f4d15005c71879a269)