Expand rendered image name to include secs and ms

Expand rendered image name to include secs and ms

The fix would avoid duplicate image names being created
when we run the builder packer jobs on both releng and
sandbox at the same time, and can potentially cause
failures while removing them in builder openstack cron job.

Creating images names timestamped upto ms reduces the probability
of name collision.

Change-Id: Ida0db499d3cdc376ab4c509614a90a8698925e0b
Signed-off-by: Anil Belur <abelur@linuxfoundation.org>