init-ceph: fix (and simplify) pushing ceph.conf to remote unique name

The old code would only do the push once per remote node (due to the
list in $pushed_to) but would reset $unique on each attempt.  This would
break if a remote host was processed twice.

Fix by just skipping the $pushed_to optimization entirely.

Fixes: #4794
Reported-by: Andreas Friedrich <andreas.friedrich@ts.fujitsu.com>
Signed-off-by: Sage Weil <sage@inktank.com>
(cherry picked from commit ccbc4dbc6edf09626459ca52a53a72682f541e86)