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>
(cherry picked from commit 6a7e20147cc39ed4689809ca7d674d3d408f2a17)