LU-8174 misc: name open file handles as such

LU-8174 misc: name open file handles as such

In a number of places in the code, rename variables from "*_handle"
or "*_fh" to "*_open_handle" so that it is clear this is referencing
an open file handle rather than something else (e.g. a lock handle).

Also rename the confusingly-named mti_close_handle to mti_open_handle,
since this is referencing an open file handle, even if it is used at
close time to close the file.

   mfd_handle2mfd() -> mfd_open_handle2mfd()
   mdt_file_data.mfd_handle -> mfd_open_handle
   mdt_file_data.mfd_old_handle -> mfd_open_handle_old
   mdt_thread_info.mti_close_handle -> mti_open_handle
   mdt_body.mbo_handle -> mbo_open_handle
   mdt_io_epoch.mio_handle -> mio_open_handle
   md_op_data.op_handle -> op_open_handle
   mdt_rec_create.cr_old_handle -> cr_open_handle_old
   mdt_reint_record.rr_handle -> rr_open_handle
   obd_client_handle.och_fh -> och_open_handle

Change the resync code path to use a "lease_handle" to avoid confusion
with an open handle:

   mdt_rec_resync.rs_handle -> rs_lease_handle
   use md_op_data.op_lease_handle
   add mdt_reint_record.rr_lease_handle

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I6e2abdaee1c32d502ea4f2f4b339a6bb21528f69
Reviewed-on: https://review.whamcloud.com/26953
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>