LU-1330 md: fix lu_ucred.c boilerplate

LU-1330 md: fix lu_ucred.c boilerplate

In preparing Ie3a3cd99 (LU-1330 obdclass: splits server-side object
stack from client) the lu_ucred infrastructure was put in its own
file.  Fixup the boilerplate of this file to give the proper path,
short description, and authors.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I77d42539c625b390cca779cb426e0125ca782d44
Reviewed-on: http://review.whamcloud.com/5910
Tested-by: Hudson
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Vitaly Fertman <vitaly_fertman@xyratex.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>