staging/lustre/mdc: fix panic at mdc_free_open()

Assertion was happened for open request when rq_replay is set
to 1.
    ASSERTION(mod->mod_open_req->rq_replay == 0)
But this situation is not fatal for client, and could happened
when mdc_close() failed.
The fix allow to free such requests. If mdc_close fail, MDS doesn`t
receive close request from client. And in a worst case client would
be evicted.

The test recreates issue when mdc_close failed and
client asserts:
   ASSERTION( mod->mod_open_req->rq_replay == 0 ) failed

Signed-off-by: Alexander Boyko <alexander.boyko@seagate.com>
Seagate-bug-id: MRP-3156
Reviewed-on: http://review.whamcloud.com/17495
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-5282


Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>