OPS-2492 fix backwards compatibility

CHANGELOG.md

 - Role: ecommerce
-  - Added `ECOMMERCE_BROKER_TRANSPORT` and renamed `ECOMMERCE_BROKER_HOST`
-    to `ECOMMERCE_BROKER_HOSTNAME`. This is to support non-amqp brokers,
-    specifically redis. If `ECOMMERCE_BROKER_HOSTNAME` is unset it will use
-    the value of `ECOMMERCE_BROKER_HOST`, however it is recommended to update
-    your configuration to set `ECOMMERCE_BROKER_HOSTNAME` explicitly.
+  - Added `ECOMMERCE_BROKER_TRANSPORT` with a default value of 'ampq' to be backwards compatible with rabbit.  Set to 'redis' if you wish to use redis instead of rabbit as a queue for ecommerce.
 
 - Role: credentials
   - This role is now dependent on the edx_django_service role. Settings are all the same, but nearly all of the tasks are performed by the edx_django_service role.

playbooks/roles/ecommerce/defaults/main.yml

@@ -146,10 +146,9 @@ ECOMMERCE_STATICFILES_STORAGE: 'ecommerce.theming.storage.ThemeStorage'
 ECOMMERCE_BROKER_USERNAME: 'celery'
 ECOMMERCE_BROKER_PASSWORD: 'celery'
 ECOMMERCE_BROKER_HOST: '{{ ansible_default_ipv4.address }}'
-ECOMMERCE_BROKER_HOSTNAME: '{{ ECOMMERCE_BROKER_HOST }}'
 ECOMMERCE_BROKER_PORT: 5672
 ECOMMERCE_BROKER_TRANSPORT: 'amqp'
-ECOMMERCE_BROKER_URL: '{{ ECOMMERCE_BROKER_TRANSPORT }}://{{ ECOMMERCE_BROKER_USERNAME }}:{{ ECOMMERCE_BROKER_PASSWORD }}@{{ ECOMMERCE_BROKER_HOSTNAME }}:{{ ECOMMERCE_BROKER_PORT }}'
+ECOMMERCE_BROKER_URL: '{{ ECOMMERCE_BROKER_TRANSPORT }}://{{ ECOMMERCE_BROKER_USERNAME }}:{{ ECOMMERCE_BROKER_PASSWORD }}@{{ ECOMMERCE_BROKER_HOST }}:{{ ECOMMERCE_BROKER_PORT }}'
 
 ECOMMERCE_DISCOVERY_SERVICE_URL: 'http://localhost:8008'
 ECOMMERCE_ENTERPRISE_URL: '{{ ECOMMERCE_LMS_URL_ROOT }}'