mgr/ansible: RGW service

mgr/ansible: RGW service

RGW basic implementation

- Add one or more hosts running RGW daemon
- Allow to specify a multisite/multizone settings using a config file.
- Remove RGW daemon used to provide service for one zone.

Comments:

I see two use cases:

a. Install/Remove in new hosts the RGW daemons and configure them.
b. RGW management (CRUD zone groups/zones ... etc)

But the current orchestrators API seems to be oriented only to cover use case b.

What i have implemented in this moment covers use case a, despite the API is not friendly with that. I have added the possibility of getting a config file to specify hosts and settings.

rgw-admin commands covers all the functionality for managing RGW... So probably it does not have too much sense to implement anything around RGW management in orchestrators (use case b).

My doubts are:

1. The current API covers RGW management using a default configuration (user cannot configure multisite/multizone). Is this ok?

2. Shoud we add more API endpoints to allow add RGW nodes/hosts and manage the RGW config?

---------------------------------

Modifications suggested by @epuerta:
 Mainly:
 - New Inventory group class for manage hosts in Ansible Roles inside Ansible Inventory.
 - A redundant plus sign was found by @epuerta

Signed-off-by: Juan Miguel Olmo Martínez <jolmomar@redhat.com>