refstack client: manually running improvement

refstack client: manually running improvement

JIRA: FUNCTEST-758

1.python tempest_conf.py can generate a reference tempest.conf under /hom/opnfv/.../refstack_client
  this is based on "rally verify configure-verifier"
  surely, user can define his/her own tempest.conf by not using this
2.python refstack_client.py -c <tempest_conf_path> --testlist <testlist_file_path>
  if not given, will use default path, if file not exists, will have error

Change-Id: I1ceecbe8fe86fbe0d53b736a0f3b9a9ae01f262f
Signed-off-by: MatthewLi <matthew.lijun@huawei.com>
(cherry picked from commit 678d5f956b1af373f61f97187ff3e66fdb315654)