ceph-dashboard: remove rgw api host,port,scheme

ceph-dashboard: remove rgw api host,port,scheme

We don't need to have dedicated variables for the RGW integration into
the Ceph Dashboard and need to be manually filled.
Instead we can use the current values from the RGW nodes by using the
IP and port from the first RGW instance of the first RGW node via the
radosgw_address and radosgw_frontend_port variables.
We don't need to specify all RGW nodes, this will be done automatically
with one node.
The RGW api scheme is using the radosgw_frontend_ssl_certificate variable
to determine if the value is http or https. This variable is also reuse
as a condition for the ssl verify task.

Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>