Fix tempest.conf generation
Fix tempest.conf generation

[service_available] isn't being generated. This patch fixes it.

Change-Id: Ib188c684b8dc41e7918075bb398776870a3f1c31
Closes-Bug: #1613542

ArchiFleKs/magnum,openstack/magnum,openstack/magnum,ArchiFleKs/magnum