Some variables like tempestmail_log_server and tempest_track_resources
are no longer required because it belongs to validate-tempest role, that
is deprecated now. Other variables like tempest_test_image_path and
tempest_tempest_conf_overrides should be used only when required. In the
case of these testenv, this is overriding what is in tempest.yml task in
tripleo-quickstart-extras, making it hard to change cirros image.
Removing here will have no impact, and all common tempest variables
should indeed be centralized in tempest.yml task.
Change-Id: I66da92fcabf204ab9ed3653132ee5221c220c5a0
e0f47848c1