Update the diskimage-create.sh to have a "-l" option to pass into
dib's "--logfile" option. In the devstack job, use this to redirect
the dib output to a separate logfile. Turn on verbose logging by
default for this log.
Copy this in the v1 jobs. v2 jobs are covered by a similar change in
octavia-tempest-plugin: I5bc0d9a3b071733cbe31d618f7236a3c2285b3e5
Depends-On: https://review.openstack.org/612865
Change-Id: Ie639af4266152d4626f8312b1849deeba5048348
5bec6f70c2