Bump timeout on stable check tempest jobs

For jobs like check-tempest-devstack-vm-*-stable-*, increase the
timeout to 90 minutes from 60.  90 matches the current timeout
for the stable-grizzly periodic checks.

Change-Id: I6df18f4f8a94ea53b4057db2382287d1b69d74c7
Merge "Bump timeout on stable check tempest jobs"