LU-16901 utils: l_getidentity with nss module support

LU-16901 utils: l_getidentity with nss module support

Enable l_getidenity to fetch user's supplementary groups
info from NIS, LDAP and/or any other services that NSS modules
exist for.

Add support for local lustre specific users in
  /etc/lustre/passwd
  /etc/lustre/group

Specify the list of modules to be searched, in-order which
allows lookup options to skip group or user searches for
particular user(s) and group(s).

To enable this feature add "lookup <mod1> <mod2> ... <modN>"
as the first line to:
  /etc/lustre/perm.conf

An example usage:
[/etc/lustre/perm.conf]
lookup lustre ldap

[/etc/lustre/passwd]
root:x:0:0:root:/root:/bin/bash

[/etc/lustre/group]
root:x:0:root

The special users in /etc/lustre do not incur the
expense of ldap queries.
Other special users like nobody, anon, etc. may be
useful to have on a cluster but not present in ldap, nis, ...

HPE-bug-id: MRP-1137, MRP-2132, LUS-2503, LUS-2453
Test-Parameters: trivial
Signed-off-by: Alexander Zarochentsev <alexander.zarochentsev@hpe.com>
Signed-off-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Change-Id: I55387e1df08bf2786ab78740403a1daf5a718d64
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/51329
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andrew Perepechko <andrew.perepechko@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>