Fix how extensions are written into tempest.conf
Fix how extensions are written into tempest.conf

compute was using the wrong name for the list of extensions.
object-store extensions were not getting written due to an inconsistency
in the swift section naming inside tempest.conf.

Change-Id: I557e07315b1a0810f829c37249ea9292454bb656

eggmaster/tempest,eggmaster/tempest,danielmellado/tempest,danielmellado/tempest