Make sure ceilometer/service_credentials wotks with internalURL

When configuring kolla with

 - kolla_enable_tls_external: "yes"

ceilometer service credential defaults to publicURL.

Ceilometer should work with the internal interface (v3 API Identity syntax):

.....
[service_credentials]
interface = internal
.....

Change-Id: I898ffb2b901f08b810756d80dbb988d8c9298219
Closes-Bug: #1643860

ansible/roles/ceilometer/templates/ceilometer.conf.j2

@@ -52,6 +52,7 @@ project_name = service
 project_domain_id = default
 user_domain_id = default
 auth_type = password
+interface = internal
 
 {% if ceilometer_database_type == 'gnocchi' %}
 [dispatcher_gnocchi]