doc: update OpenGPGCheck in a-a-save-package-data rhbz#997922

... and trusted GPG keys are stored in gpg_keys.conf

jfilak:
I've accidentally applied wrong patch. This one completes the previous one.

Signed-off-by: Richard Marko <rmarko@redhat.com>
Signed-off-by: Jakub Filak <jfilak@redhat.com>