After closer review of available configuration
options for tempest it turns out that most of them
can be safely removed from custom tempest.conf held
in devstack/files/tempest.conf leaving only those
that are trully required.
Closes-bug: #1649174
Follow-up: I9c82e9d8c1f7db088a4b99ee82d8b2b3840364d4
Needed-by: Iae561b0c7e6b90cc7c9f5b122c0e4b37bc5ef843
Change-Id: I2a1f14df0459d042fc6cd9d8778a62369aa7615a
421fe123b7