cephadm: fix a typo
this adds a space in order to avoid displaying this:
```
"2021-03-29T10:51:32.595782Z service:rgw.default [ERROR] \"Failed while placing rgw.default.ceph-vasi-node5-osd-rgw-iscsi-gw.hpuesfon ceph-vasi-node5-osd-rgw-iscsi-gw
```
instead of:
```
"2021-03-29T10:51:32.595782Z service:rgw.default [ERROR] \"Failed while placing rgw.default.ceph-vasi-node5-osd-rgw-iscsi-gw.hpuesf on ceph-vasi-node5-osd-rgw-iscsi-rgw
```
Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>
(cherry picked from commit
a3cb119a7a5134e7a3e4006381da14ea2a927136)