qa/standalone/mon/mon_cluster_log.sh: retry check for log line

qa/standalone/mon/mon_cluster_log.sh: retry check for log line

Issue: The test was failing as we were checking for the osd boot
log before it was actually emitted in the log file.

Solution: We retry checking for the desired string in the log file
for a duration of 60s after OSD has come up successfully.

Fixes: https://tracker.ceph.com/issues/67282
Signed-off-by: Shraddha Agrawal <shraddha.agrawal000@gmail.com>
Signed-off-by: Naveen Naidu <naveennaidu479@gmail.com>