Use env var for gnunet image

.gitlab-ci.yml

@@ -7,6 +7,8 @@ variables:
   IMAGE: $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA
   # To have a common name that can be referenced from other job
   RELEASE_IMAGE: $CI_REGISTRY_IMAGE:latest
+  # XXX: Change to "official" gnunet image if/when there's one
+  GNUNET_IMAGE: registry.gitlab.com/juga0/gnunet
 
 # The following are jobs to create the dockerimage from docker with the
 # gitlab runner.

docker-compose.yml

@@ -2,8 +2,7 @@ version: '3'
 
 services:
   authority.pep.example:
-    # XXX: Change to "official" gnunet image if/when there's one
-    image: registry.gitlab.com/juga0/gnunet
+    image: ${GNUNET_IMAGE:-gnunet}
     container_name: authority.pep.example
     hostname: authority
     domainname: pep.example
@@ -17,7 +16,7 @@ services:
     restart: unless-stopped
 
   gnunet.n1.pep.example:
-    image: registry.gitlab.com/juga0/gnunet
+    image: ${GNUNET_IMAGE:-gnunet}
     container_name: gnunet.n1.pep.example
     hostname: gnunet
     domainname: n1.pep.example