LU-18524 utils: Improve lctl nodemap_modify interface

LU-18524 utils: Improve lctl nodemap_modify interface

"lctl nodemap_modify" uses two separate parameters for the property
name and the corresponding value. This patch slightly improves this
interface by allowing "=value" as part of --property similar to "lctl
set_param" commands:

lctl nodemap_modify --name nm_0 --property admin=1

instead of (which is still allowed):

lctl nodemap_modify --name nm_0 --property admin --value 1

sanity-sec fileset_test_setup() was modified to exercise this
interface.

Test-Parameters: trivial testlist=sanity-sec
Signed-off-by: Marc Vef <mvef@whamcloud.com>
Change-Id: I030e1602a67c066e6daf4187589a77c1b49ee855
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/57448
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>