pki: Add a script to extract parts from a PKCS#12

Add a script pki-pkcs12-extract.sh to extract the key and/or cert
from a PKCS#12 file, with or without encryption (for the key).

Change the setup code to use it.

Change-Id: Ica596fe3ef4e5f0a60ae99b0934b10433b9d5023
Signed-off-by: Yedidyah Bar David <didi@redhat.com>