ipaserver: Fix use of subject_validator in ipaserver_test

subject_validator and also VALID_SUBJECT_ATTRS are provided of the ca
binding.

Fixes issue #43

roles/ipaserver/library/ipaserver_test.py

@@ -500,7 +500,7 @@ def main():
 
     # ca_subject
     if options.ca_subject:
-        subject_validator(VALID_SUBJECT_ATTRS, options.ca_subject)
+        ca.subject_validator(ca.VALID_SUBJECT_ATTRS, options.ca_subject)
 
     # IPv6 and SELinux check