Remove pkcs12 handling functions from CertDB
    
    These functions don't require anything from the CertDB instance,
    move them out so no needless instantiation of CertDB is performed
    in order to use them.
    
    https://fedorahosted.org/freeipa/ticket/5695
    
    Reviewed-By: Jan Cholasta <jcholast@redhat.com>