glusterd: Refresh glusterd-syncop fixes from master

Following commits were cherry-picked from master,
044f8ce syncop: Remove task from synclock's waitq before 'wake'
cb6aeed glusterd: Give up big lock before performing any RPC
46572fe Revert "glusterd: Fix spurious wakeups in glusterd syncops"
5021e04 synctask: implement barriers around yield, not the other way
4843937 glusterd: Syncop callbks should take big lock too

Change-Id: I5ae71ab98f9a336dc9bbf0e7b2ec50a6ed42b0f5
BUG: 948686
Signed-off-by: Krishnan Parthasarathi <kparthas@redhat.com>
Reviewed-on: http://review.gluster.org/4938
Reviewed-by: Amar Tumballi <amarts@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/5021
Reviewed-by: Vijay Bellur <vbellur@redhat.com>