XenAPI: support ceilometer service

This to support configuration on ceilometer services for XenAPI.
1. set hypervisor_inspector as xenapi
2. Confiugre the section of [xenapi] for XenAPI connection

For details, please refer to the config doc:
https://docs.openstack.org/ceilometer/latest/configuration/index.html

Change-Id: I4fc649d927031886c694507b3e8a686646a61ef7
blueprint: xenserver-support

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

@@ -11,6 +11,8 @@ evaluation_interval = 300
 
 {% if nova_compute_virt_type == 'vmware' %}
 hypervisor_inspector = vsphere
+{% elif nova_compute_virt_type == 'xenapi' %}
+hypervisor_inspector = xenapi
 {% endif %}
 
 [keystone_authtoken]
@@ -57,3 +59,10 @@ transport_url = {{ notify_transport_url }}
 [oslo_policy]
 policy_file = {{ ceilometer_policy_file }}
 {% endif %}
+
+{% if nova_compute_virt_type == 'xenapi' %}
+[xenapi]
+connection_url = {{ xenserver_connect_protocol }}://{{ xenserver_himn_ip }}
+connection_username = {{ xenserver_username }}
+connection_password = {{ xenserver_password }}
+{% endif %}