Add job to auto-update new built packer images

Add job to auto-update new built packer images

The job auto-updates packer images to the latest once they are built
every month into the releng/builder repository and push a commit
to Gerrit. The CR can be merged and reduces the wait time when we
want images to be updated.

Steps followed:
1. Get a list of images from the releng/builder repository
2. Search openstack cloud for the latest images available
3. Compare the time stamps of the new image with the image in use
4. Update the image to the config files and yaml files
5. Push the change to Gerrit

Change-Id: I592219df0ad5eb916448b4c905931b354f407611
Signed-off-by: Anil Belur <abelur@linuxfoundation.org>