Use testr directly in tempest verifier

Script `run_tempest.sh` writes needed records into environment and
parses arguments for transmission them to testr.
It is difficult to control arguments which passed into testr by
this script. Therefore, it would be nice if rally will use testr directly.

Blueprint tempest-verification
Closes-Bug: #1297328

Change-Id: Ia06334b1d150f2ac12720d4d238e98c922ed20f0
Merge "Use testr directly in tempest verifier"