pki: remove usage of /ca.crt uri

we have new servlet that can serve resources, so we can use this servlet
instead of per resource URI.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=961677
Change-Id: Iac544335e1a0c01388eae23405d83bdac4704d34
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>