Make the default localhost.

Override for docker in the docker overrides.

docker/build/course_discovery/ansible_overrides.yml

 ---
-course_discovery_gunicorn_host: 0.0.0.0
\ No newline at end of file
+course_discovery_gunicorn_host: 0.0.0.0
+COURSE_DISCOVERY_MYSQL: 'localhost'

playbooks/roles/course_discovery/defaults/main.yml

@@ -20,7 +20,7 @@ COURSE_DISCOVERY_NGINX_PORT: 18381
 COURSE_DISCOVERY_SSL_NGINX_PORT: 48381
 
 COURSE_DISCOVERY_DEFAULT_DB_NAME: 'course_discovery'
-COURSE_DISCOVERY_MYSQL: 'db'
+COURSE_DISCOVERY_MYSQL: 'localhost'
 # MySQL usernames are limited to 16 characters
 COURSE_DISCOVERY_MYSQL_USER: 'course_discov001'
 COURSE_DISCOVERY_MYSQL_PASSWORD: 'password'

util/jenkins/ansible-provision.sh

@@ -172,7 +172,6 @@ PROGRAMS_VERSION: $programs_version
 COURSE_DISCOVERY_NGINX_PORT: 80
 COURSE_DISCOVERY_SSL_NGINX_PORT: 443
 COURSE_DISCOVERY_VERSION: $course_discovery_version
-COURSE_DISCOVERY_MYSQL: 'localhost'
 
 NGINX_SET_X_FORWARDED_HEADERS: True
 EDX_ANSIBLE_DUMP_VARS: true