LU-15625 sec: fix set_param -P for root squash

lctl set_param -P needs to be fixed for root squash in order
to properly propagate to clients.
On server (MDT) side, the paramaters are mdt.*.*squash*.
On client side, the parameters are llite.*.*squash*.
So if the setting on MGS side is done as
set_param -P *.*.root_squash and
*.*.nosquash_nids, it works fine. But if it is done as
set_param -P mdt.*.root_squash, this setting is not applied to
client side.
The solution is to have the settings translated into
*.*.root_squash and *.*.nosquash_nids to make both sides happy.

Also, to ensure client vs. server consistency, prevent
set_param -P llite.*.root_squash.

Lustre-change: https://review.whamcloud.com/46739
Lustre-commit: 7b8449e8f9ed310376a191ec8dfa2f1cb6233377

Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I8984c9d9024d7a053e548ed15d1321b281d9940f
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/47792
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>