dashboard: use existing variable to detect containerized deployment

dashboard: use existing variable to detect containerized deployment

there is no need to add more complexity for this, let's use
`containerized_deployment` in order to detect if we are running a
containerized deployment.
The idea is to use `container_exec_cmd` the same way we do in the rest of
the playbook to run the different ceph commands needed to deploy the
ceph-dashboard role.

Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>
(cherry picked from commit 742bb6214c806cb7db1f1ea54276aecf0bf22049)