Use global job for building docker image

Change-Id: Iaa832b5de5f7e8a0f6bcd44513f675195d4a897e
Story: 2001694
Task: 23214

.zuul.yaml

@@ -9,6 +9,7 @@
       - release-notes-jobs-python3
     check:
       jobs:
+        - docker-build-monasca-service
         - monasca-tempest-python2-influxdb:
             voting: false
         - monasca-tempest-python3-influxdb:

docker/build_image.sh

@@ -44,6 +44,10 @@ set -eo pipefail  # Exit the script if any statement returns error.
 # to provide it as in the following example:
 #   $ ./build_image.sh master master refs/changes/19/595719/3
 
+# Go to folder with Docker files.
+REAL_PATH=$(python -c "import os,sys; print(os.path.realpath('$0'))")
+cd "$(dirname "$REAL_PATH")/../docker/"
+
 [ -z "$DOCKER_IMAGE" ] && \
     DOCKER_IMAGE=$(\grep DOCKER_IMAGE Dockerfile | cut -f2 -d"=")