Expand rendered image name to include secs and ms

Expand rendered image name to include secs and ms

Expand rendered image name to include seconds and milliseconds. This
reduces the probability of image name collisions on the cloud from 1/60
to 1/60000. Fixed upstream in common-packer [1.].

[1.] https://gerrit.linuxfoundation.org/infra/#/c/10986/

https://jira.linuxfoundation.org/browse/RELENG-971

Change-Id: If8a808681be6e4dea942e6f928628e57f4f1090d
Signed-off-by: Anil Belur <abelur@linuxfoundation.org>