LU-14797 sec: add projid to nodemap

LU-14797 sec: add projid to nodemap

Add the ability to create id maps of a new type, projid. This also
requires adding a new value to map_mode, projid_only. Finally, a new
property named squash_projid is used to map all project ID to a
default one.
Update lctl man pages to mention these additions.
Update sanity-sec test_12 and test_15 to exercise projid mapping and
squash_projid property.

Lustre-change: https://review.whamcloud.com/44108
Lustre-commit: 8a770616a5ad21360ecba63c3643cadd245a2a50

Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I63eba8b0d33feaa7ece8c1788cb587fcb330357a
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/45486
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>