mds: add projected rename's subtree bounds to ESubtreeMap

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
mds: fix 'discover' handling in the rejoin stage

If the MDS is the resolve stage, current MDCache::handle_discover() only handles
'discover' from MDS that it has already gotten rejoin acknowledgement. This can
cause circular wait because MDCache::rejoin_gather_finish() fetches reconnected
inodes before send rejoin acknowledgements, and fetching reconnected inode may
triggers 'discover'. The fix is not delay handling 'discover' from MDS that are
also in the rejoin stage.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
mds: allow handling slave request in the clientreplay stage

replaying a client request may need to create slave request and the slave
MDS can be also in the clientreplay stage.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
mds: mark export bounds for cross authority directory rename

this guarantees that the importing MDS gets directory fragment's
up-to-date fragstat/rstat.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
mds: clear inode dirty after slave rename finishes.

The inode is linked to a non-auth directory, so remove it from LogSegment's
dirty inode list.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>