make run.sh Linux compatible

`docker-machine` is not relevant for Linux distros so it doesn't exists in Ubuntu for example. Consequently the script hangs in infinite loop because `nc` command is invalid with an empty `DOCKER_IP�`.

run.sh

@@ -8,6 +8,9 @@ mvn clean install
 # Export the active docker machine IP
 export DOCKER_IP=$(docker-machine ip $(docker-machine active))
 
+# docker-machine doesn't exist in Linux, assign default ip if it's not set
+DOCKER_IP=${DOCKER_IP:-0.0.0.0}
+
 # Remove existing containers
 docker-compose stop
 docker-compose rm -f
@@ -38,4 +41,4 @@ done
 docker-compose up -d
 
 # Attach to the log output of the cluster
-docker-compose logs
+docker-compose logs