LU-7854 gss: install lgssc.conf under /etc/request-key.d/

LU-7854 gss: install lgssc.conf under /etc/request-key.d/

GSS keys for Lustre are generated via the lgss_keyring user-space
tool. But request-key system tool needs to know how to call
lgss_keyring in order to generate keys for Lustre.
This is done by adding the file lgssc.conf file under
/etc/request-key.d/, with the following content:
create lgssc * * /usr/sbin/lgss_keyring %o %k %t %d %c %u %g %T %P %S

This file is not packaged if gss keyring is explicitely disabled at
configure time.

Test-Parameters: trivial
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: Ibf2eb04584f6a100a57bf00070335cf4cf2c620c
Reviewed-on: https://review.whamcloud.com/31317
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Jeremy Filizetti <jeremy.filizetti@gmail.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>