Fix error detected by coverity.

Signed-off-by: Peter Jones <pjones@redhat.com>
One more tweak for RHEL signing rules.

It never ends.

Signed-off-by: Peter Jones <pjones@redhat.com>
Allow some commands to proceed without a NSS db

The NSS db is not necessary to calculate the hash, to show the
signature or to export the signed attributes.

Signed-off-by: Gary Ching-Pang Lin <glin@suse.com>