Add standalone nailgun role

Contains modifications to specify rabbitmq and
cobbler servers to allow nailgun to communicate
these servers located on different host IPs.

Additional parameters for nailgun settings are
now explicitly passed to nailgun::venv class.
Previously they were visible only due to implict
scoping.

blueprint fuel-containerization-of-services

Change-Id: I0c43bfb74f306830d8df9fc1f66096309faed369
Merge "Add standalone nailgun role"