ceph: drop extra open file reference in ceph_atomic_open()

ceph_atomic_open() calls ceph_open() after receiving the MDS reply.
ceph_open() grabs an extra open file reference. (The open request
already holds an open file reference)

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
ceph: don't grabs open file reference for aborted request

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
ceph: flush cap release queue when trimming session caps

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