LUDOC-33: fixed identity information upcall 2.x

LUDOC-33: fixed identity information upcall 2.x

Pre 2.x, Lustre used the user identity information upcall on Lustre MDS side is
through the /proc interface: /proc/fs/lustre/mds/{mdsname}/group_upcall

From 2.x: interface has been replaced (since Lustre-2.0 release) by:
/proc/fs/lustre/mdt/{mdtname}/identity_upcall, and this interface has been
superseded by lctl set_param mdt.{mdtname}.identity_info={path}. "NONE" means
no identity_upcall.

In addition, the following substitutions have been made for Lustre 2.x
"group_info" becomes "identity_info"
"mds_grp_downcall_data" becomes "identity_downcall_data"
"l_getgroups" becomes "l_getidentity"

Signed-off-by: Richard Henwood <rhenwood@whamcloud.com>
Change-Id: I9db35e8882834f4df234f38f13a55fbb1d79a377