do not try to cleanup build image on CI

circle.yml

@@ -2,7 +2,7 @@ machine:
   environment:
     GOPATH: $HOME/.go_workspace
     REPO: ${GOPATH}/src/github.com/${CIRCLE_PROJECT_USERNAME}/${CIRCLE_PROJECT_REPONAME}
-    DOCKER_VERSION: 1.10.0
+    DOCKER_VERSION: 1.9.1
     DOCKER_MACHINE_VERSION: 0.6.0
     GO15VENDOREXPERIMENT: 1
   post:

tests/build_tool.sh

@@ -51,4 +51,9 @@ fi
 # Cleanup
 rm $REPO/target/docker/burrow.dockerartefact
 rm $REPO/target/docker/burrow-client.dockerartefact
-docker rmi -f $IMAGE:build
+
+# CircleCI seems to have an issues removing this build, in any case it is not necessary on CI
+if [ ! "$CI" ]
+then
+  docker rmi -f $IMAGE:build
+fi