Exclude git dependency from Docker

Docker comes with a dependency from the native git
package. However, the one downloaded from the distro
could not be the desired version. Make sure that the
installation of Docker doesn't change the current
git setup by excluding the git package explicitly.

Change-Id: Ia1873372e76601f060e18d92f43e0f4379ee9770
diff --git a/jenkins-docker/slave-bazel-docker/Dockerfile b/jenkins-docker/slave-bazel-docker/Dockerfile
index 1dc5f66..0bc9601 100644
--- a/jenkins-docker/slave-bazel-docker/Dockerfile
+++ b/jenkins-docker/slave-bazel-docker/Dockerfile
@@ -6,4 +6,4 @@
       $(lsb_release -cs) \
       stable" && \
     apt-get update && \
-    apt-get install -y docker-ce
+    apt-get install -y docker-ce git-