decouple image name and docker user

.gitlab-ci.yml

 variables:
+  IMAGE_ORG: xpub
   IMAGE_NAME: xpub
   BASE_DOMAIN: gateway.xpub.semioticsquares.com
   CONFIGURATION_REPOSITORY: https://gitlab.coko.foundation/pubsweet/infra.git
@@ -18,11 +19,11 @@ build:
     - docker version
     - docker login -u $DOCKERHUB_USERNAME -p $DOCKERHUB_PASSWORD
     - echo "Ignore warning! Cannot perform an interactive login from a non TTY device"
-    - docker build -t $DOCKERHUB_USERNAME/$IMAGE_NAME:$CI_COMMIT_SHA .
-    - docker push $DOCKERHUB_USERNAME/$IMAGE_NAME:$CI_COMMIT_SHA
+    - docker build -t $IMAGE_ORG/$IMAGE_NAME:$CI_COMMIT_SHA .
+    - docker push $IMAGE_ORG/$IMAGE_NAME:$CI_COMMIT_SHA
 
 lint:
-  image: $DOCKERHUB_USERNAME/$IMAGE_NAME:$CI_COMMIT_SHA
+  image: $IMAGE_ORG/$IMAGE_NAME:$CI_COMMIT_SHA
   stage: test
   variables:
     GIT_STRATEGY: none
@@ -31,7 +32,7 @@ lint:
     - npm run lint
 
 test:
-  image: $DOCKERHUB_USERNAME/$IMAGE_NAME:$CI_COMMIT_SHA
+  image: $IMAGE_ORG/$IMAGE_NAME:$CI_COMMIT_SHA
   stage: test
   variables:
     GIT_STRATEGY: none