Catch errors on config duplication command

test/mail_with_postgrey_disabled_by_default.bats

@@ -1,11 +1,13 @@
 load 'test_helper/common'
 
 function setup() {
+    local PRIVATE_CONFIG
+    PRIVATE_CONFIG="$(duplicate_config_for_container .)"
     CONTAINER=$(docker run -d \
-		-v "$(duplicate_config_for_container .)":/tmp/docker-mailserver \
-		-v "$(pwd)/test/test-files":/tmp/docker-mailserver-test:ro \
-		-e DMS_DEBUG=0 \
-		-h mail.my-domain.com -t ${NAME})
+                          -v "${PRIVATE_CONFIG}":/tmp/docker-mailserver \
+                          -v "$(pwd)/test/test-files":/tmp/docker-mailserver-test:ro \
+                          -e DMS_DEBUG=0 \
+                          -h mail.my-domain.com -t ${NAME})
     # using postfix availability as start indicator, this might be insufficient for postgrey
     wait_for_smtp_port_in_container $CONTAINER
 }