Allow bind and nginx to be different
This introduces a pulp_api_bind variable in the 'pulp' playbook which
the user can use to set the bind address (or multiple) of pulp-api. This
is used by the pulp-api service template for the systemd service.
It moves the nginx and apache reverse proxy variables out of the 'pulp'
playbook and into the 'pulp-webserver' playbook where they are used
exclusively. The defaults are there also. It created 4 variables: