LU-2607 mdd: preserve input arguments in mdd_create()

all input arguments are supposed to stay as is so that
the caller can re-use them again.

Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Change-Id: Ie2be78e702bfa9b7febafe7d106f09beccbf48d3
Reviewed-on: http://review.whamcloud.com/5048
Reviewed-by: wangdi <di.wang@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>