ipatests: Tracker implementation for Sub CA feature

The patch implements Tracker subclass for CA plugin
and the basic CRUD tests for the plugin entries.

https://fedorahosted.org/freeipa/ticket/4559

Reviewed-By: Fraser Tweedale <ftweedal@redhat.com>

ipatests/test_xmlrpc/objectclasses.py

@@ -222,3 +222,8 @@ caacl = [
     u'ipaassociation',
     u'ipacaacl'
 ]
+
+ca = [
+    u'top',
+    u'ipaca',
+]