init-ceph: continue after failure doing osd data mount

If we are starting many daemons and hit an error, we normally note it and
move on.  Do the same when doing the pre-mount step.

Fixes: #8554
Signed-off-by: Sage Weil <sage@inktank.com>
Merge pull request #1936 from ceph/wip-8554

init-ceph: continue after failure doing osd data mount

Reviewed-by: Loic Dachary <loic@dachary.org>