Disable list_extend in config_template

This allow ceilometer pipelines to be fully controlled with config_template.
Previously a ceilometer pipeline would extend a nested list instead of
redefining it which can have undesirable effects. This change disables the
default list_extend property within the config_template allowing a deployer
to fully redefine a given pipeline.

Change-Id: Ibe64254dcbca99b6b720146d2d4f2a25e22236a3
Signed-off-by: Kevin Carter <kevin.carter@rackspace.com>

releasenotes/notes/disable-list-extend-3a9547de9034f9ba.yaml

@@ -0,0 +1,10 @@
+---
+features:
+  - Yaml files used for ceilometer configuration will now allow a deployer to
+    override a given list. If an override is provided that matches an already
+    defined list in one of the ceilometer default yaml files the entire list
+    will be replaced by the provided override. Previously, a nested lists of
+    lists within the default ceilometer configration files would extend should
+    a deployer provide an override matching an existing pipeline. The
+    extension of the defaults had a high probability to cause undesirable
+    outcomes and was very unpredictable.

tasks/ceilometer_post_install.yml

@@ -22,6 +22,7 @@
     mode: "0644"
     config_overrides: "{{ item.config_overrides }}"
     config_type: "{{ item.config_type }}"
+    list_extend: "{{ item.list_extend | default(omit) }}"
   with_items:
     - src: "ceilometer.conf.j2"
       dest: "/etc/ceilometer/ceilometer.conf"
@@ -41,26 +42,32 @@
       dest: "/etc/ceilometer/event_pipeline.yaml"
       config_overrides: "{{ ceilometer_event_pipeline_yaml_overrides }}"
       config_type: "yaml"
+      list_extend: false
     - src: "event_definitions.yaml.j2"
       dest: "/etc/ceilometer/event_definitions.yaml"
       config_overrides: "{{ ceilometer_event_definitions_yaml_overrides }}"
       config_type: "yaml"
+      list_extend: false
     - src: "pipeline.yaml.j2"
       dest: "/etc/ceilometer/pipeline.yaml"
       config_overrides: "{{ ceilometer_pipeline_yaml_overrides }}"
       config_type: "yaml"
+      list_extend: false
     - src: "gnocchi_resources.yaml.j2"
       dest: "/etc/ceilometer/gnocchi_resources.yaml"
       config_overrides: "{{ ceilometer_gnocci_resources_yaml_overrides }}"
       config_type: "yaml"
+      list_extend: false
     - src: "osprofiler_event_definitions.yaml.j2"
       dest: "/etc/ceilometer/osprofiler_event_definitions.yaml"
       config_overrides: "{{ ceilometer_osprofiler_event_definitions_yaml_overrides }}"
       config_type: "yaml"
+      list_extend: false
     - src: "loadbalancer_v2_meter_definitions.yaml.j2"
       dest: "/etc/ceilometer/loadbalancer_v2_meter_definitions.yaml"
       config_overrides: "{{ ceilometer_loadbalancer_v2_meter_definitions_yaml_overrides }}"
       config_type: "yaml"
+      list_extend: false
     - src: "policy.json.j2"
       dest: "/etc/ceilometer/policy.json"
       config_overrides: "{{ ceilometer_policy_overrides }}"