LU-8813 gss: allow svcgssd to start without "-k"

LU-8813 gss: allow svcgssd to start without "-k"

Previous versions of svcgssd did not require the "-k" option when
running in Kerberos mode (the only mode available).  If none of
the -k, -s, or -z options are given for enabling security flavours
then assume "-k" for compatibility reasons.

This will generate a warning before 3.1 is released, at which point
it will turn into an error.

Make the use of -s an error if SSK is not available.

Test-Parameters: trivial testlist=sanity-sec
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I9b7389bbca56d6717f02b21f57da52adc4602971
Reviewed-on: https://review.whamcloud.com/23925
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andrew Perepechko <andrew.perepechko@seagate.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: Jeremy Filizetti <jeremy.filizetti@gmail.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>