[docker_test.sh] Quotes strike again

docker_test.sh

 #!/bin/bash
 
+set -e
+
 usage() {
   echo -e "usage:\t$0 DIRECTORY, e.g. $0 pica-mattermost"
   echo -e "\tDIRECTORY : name of the directory containing docker-compose.yml\n"
@@ -82,7 +84,7 @@ done
 echo -e "\n==== Remove and re-create named external volumes ===="
 for v in $(docker-compose config --volumes); do
   res=$(grep $v -A 1 docker-compose.yml | grep 'external' || true)
-  if [ ! -z $res ]; then
+  if [ ! -z "$res" ]; then
     # Don't fail if volume does not exists
     docker volume rm "$v" || true
     docker volume create "$v"