MAN: Update description of sssctl Reviewed-by: Pavel Březina <pbrezina@redhat.com>

sssctl: manual page Resolves: https://fedorahosted.org/sssd/ticket/3055 Reviewed-by: Michal Židek <mzidek@redhat.com> Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>