supervisor-xqueue: Fix duplicate declaration of default variable `XQUEUE_BASIC_AUTH`

`XQUEUE_BASIC_AUTH` was declared twice for two different usages: activating/deactivating
the auth (boolean), and a [login, password] list. Split the second usage (login/password
list) into two separate variables, like the corresponding django_auth variables.

playbooks/roles/xqueue/defaults/main.yml

@@ -32,7 +32,8 @@ XQUEUE_S3_PATH_PREFIX: 'sandbox-xqueue'
 XQUEUE_LOCAL_LOGLEVEL: 'INFO'
 XQUEUE_AWS_ACCESS_KEY_ID : ''
 XQUEUE_AWS_SECRET_ACCESS_KEY : ''
-XQUEUE_BASIC_AUTH: ['edx', 'edx']
+XQUEUE_BASIC_AUTH_USER: 'edx'
+XQUEUE_BASIC_AUTH_PASSWORD: 'edx'
 XQUEUE_DJANGO_USER: 'lms'
 XQUEUE_DJANGO_PASSWORD: 'password'
 XQUEUE_RABBITMQ_USER: 'edx'
@@ -59,7 +60,7 @@ xqueue_env_config:
 xqueue_auth_config:
   AWS_ACCESS_KEY_ID:  $XQUEUE_AWS_ACCESS_KEY_ID
   AWS_SECRET_ACCESS_KEY: $XQUEUE_AWS_SECRET_ACCESS_KEY
-  REQUESTS_BASIC_AUTH: $XQUEUE_BASIC_AUTH
+  REQUESTS_BASIC_AUTH: [$XQUEUE_BASIC_AUTH_USER, $XQUEUE_BASIC_AUTH_PASSWORD]
   USERS: { '{{XQUEUE_DJANGO_USER}}' : $XQUEUE_DJANGO_PASSWORD }
   DATABASES:
     default: