Add slave-bazel-docker image to central Makefile

The slave-bazel-docker image was not built, when using the central
Makefile, which allowed to build all docker images in sequence.

Change-Id: I7d5feee5fb00d19be77454f6052cca67dfe0535d
diff --git a/jenkins-docker/Makefile b/jenkins-docker/Makefile
index 5e22013..2d2fa6e 100644
--- a/jenkins-docker/Makefile
+++ b/jenkins-docker/Makefile
@@ -1,4 +1,4 @@
-SLAVE_DIRS ?= slave-debian slave-chrome slave-node-wct slave-buck slave-bazel-nocache slave-bazel slave-sbt slave-mvn slave-release
+SLAVE_DIRS ?= slave-debian slave-chrome slave-node-wct slave-buck slave-bazel-nocache slave-bazel slave-bazel-docker slave-sbt slave-mvn slave-release
 ALL_DIRS ?= master $(SLAVE_DIRS)
 NO_CACHE ?= true