Allow tempest_tempest_conf_overrides to be defined in many variables

Combine all variables starting with tempest_tempest_conf_overrides
to give a complete set of configuration to tempest when multiple
different test scenarios are enabled at the same time.

Change-Id: Iba5e061d1682d16c0516249f628f948a20580df8

defaults/main.yml

@@ -342,6 +342,7 @@ tempest_projects:
   - "tempest"
 
 ## Tunable overrides
+tempest_tempest_conf_search_overrides_pattern: 'tempest_tempest_conf_overrides'
 tempest_tempest_conf_overrides: {}
 
 ## The name of cloud from clouds.yaml

tasks/tempest_post_install.yml

@@ -37,7 +37,7 @@
     owner: "root"
     group: "root"
     mode: "0644"
-    config_overrides: "{{ tempest_tempest_conf_overrides }}"
+    config_overrides: "{{ _tempest_tempest_conf_overrides_gathered }}"
     config_type: "ini"
   register: copy_tempest_config
   when: not tempest_use_tempestconf | bool

vars/main.yml

@@ -143,3 +143,6 @@ _tempest_test_gathered_excludelist: "{{ query('vars', *query('varnames', '^' ~ t
 # with any dynamically gathered variables
 _tempest_test_includelist: "{{ tempest_test_includelist | union(_tempest_test_gathered_includelist) }}"
 _tempest_test_excludelist: "{{ tempest_test_excludelist | union(_tempest_test_gathered_excludelist) }}"
+
+# gather tempest config overrides from any variables starting wth the defined search pattern
+_tempest_tempest_conf_overrides_gathered: "{{ query('vars', *query('varnames', '^' ~ tempest_tempest_conf_search_overrides_pattern)) | combine }}"