read password from config file instead of generating one new every time

Add role prefix to role specifig variable to avoid conflicts when
using multiples role on the same machine on the same play.

This is beacause nginx will do canonization of URIs before
proxy-passing if you add anything after the port host:port.

For example, with:

     location /anything {
          proxy_pass http://127.0.0.1:8008/anything;
     }

NGINX will perform canonization, but with:

     location /anything {
          proxy_pass http://127.0.0.1:8008
	  # With NO Trailing slash
     }

NGINX will pass the unaltered original request, included /anything, to
the upstream server.

Canonization leads to problem when federating to other matrix-synapse
instances. The observed bug was:

- User A on our server (@A:our.server) invites User B on external
server (@B:matrix.org).

- User B correctly receive the invite.

- User B try to join the room but the request timeout.

- On our.sever logs we see "signature tampered" errors related to
  incoming connection from the external server (matrix.org).

This commit fix the issue.

- User last official deb package from matrix.org

- Revised LDAP integration:
  * ldap_server, ldap_domain [ ldap_basedn ] config vraiables.
  * Bind a protected service account with a service password and
    start-tls

- Hardcoded matrix.lilik.it --> {{ ansible_hostname }}.{{ domain }}

- Sqlite -> Postgres

New variables:

- matrix_domain | default($domain)

this role variables will be used during templating
for nginx reverse proxy