Do not re-start nodes if they are already up&running

	modified:   elasticluster/cluster.py
	modified:   elasticluster/subcommands.py
Add configuration entry `image_userdata` to pass an `user_data` to the VM.
Add support for `pbs` setup class

	modified:   elasticluster/providers/setup_providers.py
Various fices on the ansible setup provider.

	modified:   elasticluster/providers/setup_providers.py