LU-2983 osd: osd-zfs to handle errors in IO path

LU-2983 osd: osd-zfs to handle errors in IO path

- handle an error returned by dmu_buf_hold_array_by_bonus():
  release already pinned buffers, return an error to the caller.
- OFD to handle an error returned by dt_bufs_get()

Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Change-Id: I1fe46364967dbc527d0d80f3729673c00ab7154c
Reviewed-on: http://review.whamcloud.com/5784
Tested-by: Hudson
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>