LU-17899 gss: lsvcgss service fix

LU-17899 gss: lsvcgss service fix

The lsvcgss service can fail to start if the daemon is invoked with
the '-k' option whereas no proper Kerberos configuration is in place
on the server. The daemon should ignore the '-k' option is such case
and try to start the other provided modes if any (SSK, Null).
And in case the daemon is started with the '-s' option (SSK), it
spawns a temporary additional thread to compute the number of rounds
used for Miller-Rabin prime testing. So the lsvcgss_sysd script should
support that.

Fixes: c6878334a1 ("LU-17741 gss: fix lsvcgss service for systemd")
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: Iba632bd0ea9696ccea52bff5982a4d4e490597a7
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/55293
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>