rolling_update: fix dest path for mgr keys fetching

rolling_update: fix dest path for mgr keys fetching

the role `ceph-mgr` that is played later in the playbook fails because
the destination path for the fetched keys is wrong.
This patch fix the destination path used in the task `fetch ceph mgr
key(s)` so there is no mismatch.

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=1574995
Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>
(cherry picked from commit 1b4c3f292d8779158ea445a8c9a11c8ed26abe11)
Signed-off-by: Sébastien Han <seb@redhat.com>