LU-8590 utils: remove duplicate code in lgss_sk

LU-8590 utils: remove duplicate code in lgss_sk

Remove the code duplication between creating a new keyfile and
modifying an existing keyfile.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: Id8f8ec535eb7e076ce70cd765e5c3c86ae686236
Reviewed-on: https://review.whamcloud.com/23722
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Jeremy Filizetti <jeremy.filizetti@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>