mds: properly wake up scatter_nudge waiters after clearing scatter dirty

mds: properly wake up scatter_nudge waiters after clearing scatter dirty

LogSegment::try_to_expire() calls Locker::scatter_nudge() for dirty
scatter locks. If lock's parent is non-auth, Locker::scatter_nudge()
waits on the stable bit of corresponding lock. There are some cases
that scatter locks get marked clean without involving lock state
transition. We need to wake up scatter_nudge waiters in these cases.

Also remove the code that clear dirty scatter locks after inode gets
imported. I can't see why we should do that.

Signed-off-by: Yan, Zheng <zyan@redhat.com>