Revert ironic-tftp to ironic-pxe image change

The container name was changed but the image was not...

Author: markgoddard

etc/kayobe/pulp.yml

@@ -447,7 +447,7 @@ stackhpc_pulp_images_kolla:
   - ironic-conductor
   - ironic-inspector
   - ironic-neutron-agent
-  - ironic-tftp
+  - ironic-pxe
   - iscsid
   - keepalived
   - keystone