rgw: enhances rgw-restore-bucket-index script

rgw: enhances rgw-restore-bucket-index script

This enhances the script to both process versioned buckets correctly
and to handle object names that begin with underscore.

If the bucket is versioned it submits each version chronologically
(based on mtime) to be reindexed in order to "replay" the modification
of objects. However mtime is not a perfect indicator. So additionally
it looks at the OLH object to determine the most recent version and
the script makes sure that it is replayed last. The order of previous
versions is likely correct, but not guaranteed to be so.

Additional logic is added to handle objects with names that begin with
underscore ('_') since that's used as a delimiter and needs to be
escaped and rados object locators are also used.

A man page for the script is added.

Signed-off-by: J. Eric Ivancich <ivancich@redhat.com>