Allow publishing to different Docker registries

Recently, Dockerhub has become very slow and unstable
due to the introduction of hard limits on pulls and
throttling.

Make the prefix for all our CI images a configurable
variable, so that it becomes easy to switch to a
different Docker registry.

Change-Id: Ida613bfd1c3d9c779d2f522431ec8f4098c7bcfa
diff --git a/jenkins-docker/bazel-cache/Makefile b/jenkins-docker/bazel-cache/Makefile
index 2623506..8fb4d04 100644
--- a/jenkins-docker/bazel-cache/Makefile
+++ b/jenkins-docker/bazel-cache/Makefile
@@ -1,5 +1,6 @@
 NO_CACHE=false
-IMAGE=gerritforge/bazel-cache
+PREFIX=gerritforge
+IMAGE=${PREFIX}/bazel-cache
 CACHE_ALLOW=0.0.0.0/0
 
 # Targets
diff --git a/jenkins-docker/slave-aws/Makefile b/jenkins-docker/slave-aws/Makefile
index d3ddc63..3f4a84c 100644
--- a/jenkins-docker/slave-aws/Makefile
+++ b/jenkins-docker/slave-aws/Makefile
@@ -1,5 +1,6 @@
 NO_CACHE=false
-IMAGE=gerritforge/gerrit-ci-slave-aws
+PREFIX=gerritforge
+IMAGE=${PREFIX}/gerrit-ci-slave-aws
 
 # Targets
 
diff --git a/jenkins-docker/slave-bazel-docker/Makefile b/jenkins-docker/slave-bazel-docker/Makefile
index e2ee20e..ab3bc4d 100644
--- a/jenkins-docker/slave-bazel-docker/Makefile
+++ b/jenkins-docker/slave-bazel-docker/Makefile
@@ -1,7 +1,8 @@
 include ../chrome-vers.mk
 
 NO_CACHE=false
-IMAGE=gerritforge/gerrit-ci-slave-bazel-docker:debian-buster
+PREFIX=gerritforge
+IMAGE=${PREFIX}/gerrit-ci-slave-bazel-docker:debian-buster
 
 # Targets
 
diff --git a/jenkins-docker/slave-bazel-nocache/Makefile b/jenkins-docker/slave-bazel-nocache/Makefile
index 92e24aa..5e37d47 100644
--- a/jenkins-docker/slave-bazel-nocache/Makefile
+++ b/jenkins-docker/slave-bazel-nocache/Makefile
@@ -1,7 +1,8 @@
 include ../chrome-vers.mk
 
 NO_CACHE=false
-IMAGE=gerritforge/gerrit-ci-slave-bazel:debian-buster-nocache
+PREFIX=gerritforge
+IMAGE=${PREFIX}/gerrit-ci-slave-bazel:debian-buster-nocache
 BAZEL_VER=4.0.0
 BUILDIFIER_VER=4.0.0
 BAZELISK_VER=1.7.4
diff --git a/jenkins-docker/slave-bazel/Makefile b/jenkins-docker/slave-bazel/Makefile
index db0d52f..0da3add 100644
--- a/jenkins-docker/slave-bazel/Makefile
+++ b/jenkins-docker/slave-bazel/Makefile
@@ -1,7 +1,8 @@
 include ../chrome-vers.mk
 
 NO_CACHE=false
-IMAGE=gerritforge/gerrit-ci-slave-bazel:debian-buster
+PREFIX=gerritforge
+IMAGE=${PREFIX}/gerrit-ci-slave-bazel:debian-buster
 
 # Targets
 
diff --git a/jenkins-docker/slave-chrome/Makefile b/jenkins-docker/slave-chrome/Makefile
index 127fcb3..e31e9e4 100644
--- a/jenkins-docker/slave-chrome/Makefile
+++ b/jenkins-docker/slave-chrome/Makefile
@@ -2,7 +2,8 @@
 
 NO_CACHE ?= false
 DEBIAN_VER ?= buster
-IMAGE=gerritforge/gerrit-ci-slave-chrome:$(DEBIAN_VER)
+PREFIX=gerritforge
+IMAGE=${PREFIX}/gerrit-ci-slave-chrome:$(DEBIAN_VER)
 
 build: Makefile Dockerfile
 	@for chrome_ver in $(CHROME_VERS); \
diff --git a/jenkins-docker/slave-debian/Makefile b/jenkins-docker/slave-debian/Makefile
index d89181d..3089f42 100644
--- a/jenkins-docker/slave-debian/Makefile
+++ b/jenkins-docker/slave-debian/Makefile
@@ -1,5 +1,6 @@
 NO_CACHE ?= false
-IMAGE=gerritforge/gerrit-ci-slave-debian
+PREFIX=gerritforge
+IMAGE=${PREFIX}/gerrit-ci-slave-debian
 MAVEN_VER=3.6.3
 GIT_VER=2.26.2
 DEBIAN_VER=buster
diff --git a/jenkins-docker/slave-jekyll/Makefile b/jenkins-docker/slave-jekyll/Makefile
index e1948e3..7089017 100644
--- a/jenkins-docker/slave-jekyll/Makefile
+++ b/jenkins-docker/slave-jekyll/Makefile
@@ -1,5 +1,6 @@
 NO_CACHE ?= false
-IMAGE=gerritforge/gerrit-ci-slave-jekyll
+PREFIX=gerritforge
+IMAGE=${PREFIX}/gerrit-ci-slave-jekyll
 
 build:  Dockerfile Makefile
 	docker build --no-cache=$(NO_CACHE) -f Dockerfile -t $(IMAGE) .
diff --git a/jenkins-docker/slave-mvn/Makefile b/jenkins-docker/slave-mvn/Makefile
index 03fc47b..217c2c3 100644
--- a/jenkins-docker/slave-mvn/Makefile
+++ b/jenkins-docker/slave-mvn/Makefile
@@ -1,5 +1,6 @@
 NO_CACHE=false
-IMAGE=gerritforge/gerrit-ci-slave-mvn
+PREFIX=gerritforge
+IMAGE=${PREFIX}/gerrit-ci-slave-mvn
 
 # Targets
 
diff --git a/jenkins-docker/slave-node-wct/Makefile b/jenkins-docker/slave-node-wct/Makefile
index 2fff934..46d3e91 100644
--- a/jenkins-docker/slave-node-wct/Makefile
+++ b/jenkins-docker/slave-node-wct/Makefile
@@ -3,7 +3,8 @@
 NO_CACHE ?= false
 NODE_VER ?= 10
 WCT_VER ?= 6.8.0
-IMAGE=gerritforge/gerrit-ci-slave-node-wct:$(NODE_VER)-$(WCT_VER)
+PREFIX=gerritforge
+IMAGE=${PREFIX}/gerrit-ci-slave-node-wct:$(NODE_VER)-$(WCT_VER)
 
 build:  Dockerfile Makefile
 	@for chrome_ver in $(CHROME_VERS); \
diff --git a/jenkins-docker/slave-python3/Makefile b/jenkins-docker/slave-python3/Makefile
index 5a717ef..0bceabc 100644
--- a/jenkins-docker/slave-python3/Makefile
+++ b/jenkins-docker/slave-python3/Makefile
@@ -1,6 +1,7 @@
 NO_CACHE ?= false
 DEBIAN_VER ?= buster
-IMAGE=gerritforge/gerrit-ci-slave-python3:$(DEBIAN_VER)
+PREFIX=gerritforge
+IMAGE=${PREFIX}/gerrit-ci-slave-python3:$(DEBIAN_VER)
 
 build:  Dockerfile Makefile
 	cat Dockerfile | DEBIAN_VER=$(DEBIAN_VER) envsubst > Dockerfile-$(DEBIAN_VER)
diff --git a/jenkins-docker/slave-release/Makefile b/jenkins-docker/slave-release/Makefile
index 42dd7e4..e8d128c 100644
--- a/jenkins-docker/slave-release/Makefile
+++ b/jenkins-docker/slave-release/Makefile
@@ -1,5 +1,6 @@
 NO_CACHE=true
-IMAGE=gerritforge/gerrit-ci-slave-bazel:debian-buster-nocache-80.0.3987.149
+PREFIX=gerritforge
+IMAGE=${PREFIX}/gerrit-ci-slave-bazel:debian-buster-nocache-80.0.3987.149
 CONTAINER=release
 
 build:
diff --git a/jenkins-docker/slave-sbt/Makefile b/jenkins-docker/slave-sbt/Makefile
index ceb6637..d2a811e 100644
--- a/jenkins-docker/slave-sbt/Makefile
+++ b/jenkins-docker/slave-sbt/Makefile
@@ -1,5 +1,6 @@
 NO_CACHE=false
-IMAGE=gerritforge/gerrit-ci-slave-bazel-sbt
+PREFIX=gerritforge
+IMAGE=${PREFIX}/gerrit-ci-slave-bazel-sbt
 
 # Targets