Create socket_group option, which gets passed in as the -G option.
Merge branch 'socket_group' of https://github.com/EvanKrall/garethr-docker into EvanKrall-socket_group

Conflicts:
	templates/etc/init/docker.conf.erb
	templates/etc/sysconfig/docker.erb
Merge branch 'EvanKrall-socket_group'