Add novalient as a dependency

Forgot to add novaclient as a depenency here.
Update packer shutdown_command

shutdown seems to not work properly on the images I was building.
therefore, move the default to halt -p.
Wait for ssh and pull the remote image when done

This change incorporated 2 fixes:
- instead of sleeping for ssh access to be available, poll for port
22 being accessible.
- once the build is done, pull the remote image locally