python3 image: use debian buster and add pipenv

This way we get a current version of python 3 via debian buster which
is required for building the homepage.

Change-Id: I92e7233e7c4bf123ad7ba4d77d364640a1ca0f8b
diff --git a/jenkins-docker/master/config.xml b/jenkins-docker/master/config.xml
index d28a8a9..90a7f58 100644
--- a/jenkins-docker/master/config.xml
+++ b/jenkins-docker/master/config.xml
@@ -193,7 +193,7 @@
           </retentionStrategy>
           <numExecutors>1</numExecutors>
           <dockerTemplateBase>
-            <image>gerritforge/gerrit-ci-slave-python3:stretch</image>
+            <image>gerritforge/gerrit-ci-slave-python3:buster</image>
             <dockerCommand></dockerCommand>
             <lxcConfString></lxcConfString>
             <hostname></hostname>
diff --git a/jenkins-docker/slave-python3/Dockerfile b/jenkins-docker/slave-python3/Dockerfile
index ba2c950..d2820e0 100644
--- a/jenkins-docker/slave-python3/Dockerfile
+++ b/jenkins-docker/slave-python3/Dockerfile
@@ -2,5 +2,5 @@
 
 RUN apt-get update && apt-get install -y \
     python3-pip && \
-    pip3 install yamllint && \
-    rm -Rf /var/lib/apt/lists
\ No newline at end of file
+    pip3 install yamllint pipenv && \
+    rm -Rf /var/lib/apt/lists
diff --git a/jenkins-docker/slave-python3/Makefile b/jenkins-docker/slave-python3/Makefile
index 2f428ca..5a717ef 100644
--- a/jenkins-docker/slave-python3/Makefile
+++ b/jenkins-docker/slave-python3/Makefile
@@ -1,5 +1,5 @@
 NO_CACHE ?= false
-DEBIAN_VER ?= stretch
+DEBIAN_VER ?= buster
 IMAGE=gerritforge/gerrit-ci-slave-python3:$(DEBIAN_VER)
 
 build:  Dockerfile Makefile