LU-8590 utils: fix minor issues in lgss_sk usage

LU-8590 utils: fix minor issues in lgss_sk usage

Print warning message if secret keyfile has permissive access mode.
Improve error messages to start with either "error:" or "warning:".

Add "--key-bits" long option for "-k", and "--integrity" for "-i".
Don't print "Prime (p):" field with "-r" if no prime key is stored.
Improve usage message and man page for lgss_sk utility.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I8c36f0f20a0144b351b51c2d25edad9c8bd0d050
Reviewed-on: http://review.whamcloud.com/23691
Tested-by: Jenkins
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>