Use specific mysql docker image, plus install_docker_compose function

Change-Id: I508d64a0e2f12587739ea159ef8687aae797e4a6
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/installers/docker/docker-compose.yaml b/installers/docker/docker-compose.yaml
index 82d0d09..01b4d66 100644
--- a/installers/docker/docker-compose.yaml
+++ b/installers/docker/docker-compose.yaml
@@ -65,7 +65,7 @@
     #  - mongo
     #  - ro
   ro-db:
-    image: mysql
+    image: mysql:5
     networks:
       - netOSM
     env_file: