Use slave-bazel-docker as default build slave

Jenkins was still configured to use slave-bazel as the default
build-slave. Thus the slave did not have access to the docker host,
which would be needed for tests using docker.

This change configures Jenkins to use slave-bazel-docker instead, which
is built on top of slave-bazel and provides docker-functionality.

Change-Id: I9526e9e00df9cf2cab8d8638677d670244d7c176
diff --git a/jenkins-docker/master/config.xml b/jenkins-docker/master/config.xml
index 2542906..c9604cf 100644
--- a/jenkins-docker/master/config.xml
+++ b/jenkins-docker/master/config.xml
@@ -58,7 +58,7 @@
           </retentionStrategy>
           <numExecutors>1</numExecutors>
           <dockerTemplateBase>
-            <image>gerritforge/gerrit-ci-slave-bazel:debian-stretch</image>
+            <image>gerritforge/gerrit-ci-slave-bazel-docker:debian-stretch</image>
             <dockerCommand></dockerCommand>
             <lxcConfString></lxcConfString>
             <hostname></hostname>