Remove use of unsupported TEMPEST_SERVICES variable
Remove use of unsupported TEMPEST_SERVICES variable

TEMPEST_SERVICES global variable is not supported
by devstack since long back.
- I380dd20e5ed716a0bdf92aa02c3730359b8136e4
- I9c24705e494689f09a885eb0a640efd50db33fcf

Service availability of tempest known services will be
set by devstack with local check.
- I02be777bf93143d946ccbb8e9eff637bfd1928d4

This commit removes the unused TEMPEST_SERVICES setting
Related-Bug: #1743688

Change-Id: Iccbc833d821a2d7b2bc34860170ce1817fbecead

openstack/trove,openstack/trove