Branch b1_8

Branch b1_8
I found a few issues after landing the patch for 18574.(some are caused by it, some are easier to
be reproduced by it)
1. in setquota, quota slaves will set their quota limitation to 1 and then get more quota. But in
this time, it's lqs size is the default value. If we have set a small quota limitation, we will
meet -EDQUOT. So we should adjust qunit firstly in this situation.
2. filter_quota_ctl(), we should promise there is no qunit is calculated or sent between
qctxt_wait_pending_dqacq() and fsfilt_quotactl(). Now I did this via a "fake" qunit.
b=18574
i=johann
i=fanyong