Branch b1_6

This patch includes att18982, att18236, att18237,att18983 and att19061 in bz14840.
Slove "quota recovery deadlock during mds failover", it includes:
1. fix osts hang when mds does failover with quotaon
2. prevent watchdog storm when osts threads wait for the
   recovery of mds
b=14840
i=johann
i=shadow
i=panda