ceph-iscsi: fix certificates generation and distribution

ceph-iscsi: fix certificates generation and distribution

Prior to this patch, the certificates where being generated on a single
node only (because of the run_once: true). Thus certificates were not
distributed on all the gateway nodes.

This would require a second ansible run to work. This patches fix the
creation and keys's distribution on all the nodes.

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=1540845
Signed-off-by: Sébastien Han <seb@redhat.com>