LU-4367 ptlrpc: add OBD_CONNECT_UNLINK_CLOSE flag

Add OBD_CONNECT_UNLINK_CLOSE flag for interop, once this is supported,
client packs file handle in unlink RPC, and MDT will close file before
unlink.

Signed-off-by: Lai Siyao <lai.siyao@intel.com>
Change-Id: If2f89a5268b95386e01cdc2f8613fd5c4cbd1d2c
Reviewed-on: http://review.whamcloud.com/10426
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>