LU-3335 osd: use local transaction directly inside OSD

LU-3335 osd: use local transaction directly inside OSD

For OSD internal function, it is unnecessay to call dt_trans_xxx for
transaction operations. Instead, call backend journal APIs directly.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I111c52f76a894e4269ad8ac6aec3ea7747ba4f59
Reviewed-on: http://review.whamcloud.com/7145
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>