Make MySQL configuration files/docs consistent

- use petclinic as the db name and root password

Fixes #322

docker-compose.yml

 mysql:
-  image: mysql
+  image: mysql:5.7
   ports:
     - "3306:3306"
   environment:
-    - MYSQL_ROOT_PASSWORD=root
-    - MYSQL_DATABASE=test
+    - MYSQL_ROOT_PASSWORD=petclinic
+    - MYSQL_DATABASE=petclinic
   volumes:
-    - "./conf.d:/etc/mysql/conf.d:ro"
\ No newline at end of file
+    - "./conf.d:/etc/mysql/conf.d:ro"

src/main/resources/application-mysql.properties

 # database init, supports mysql too
 database=mysql
-spring.datasource.url=jdbc:mysql://localhost/test
+spring.datasource.url=jdbc:mysql://localhost/petclinic
 spring.datasource.username=root
-spring.datasource.password=root
+spring.datasource.password=petclinic
 # Uncomment this the first time the app runs
 # spring.datasource.initialization-mode=always