TT#113650 Build 'buster' docker image

We still have some internal repos building 'buster' packages and
they will use 'buster' dockers for testing based on $distribution
option. So let's build also buster image for tap-tests.

Change-Id: Ibb3c021fa4ad7856564f02687df028833c5aa983

t/tap-tests-docker/Dockerfile

@@ -1,11 +1,11 @@
-# DOCKER_NAME=jenkins-tap-test-bullseye
-FROM docker.mgm.sipwise.com/sipwise-bullseye:latest
+# DOCKER_NAME=jenkins-tap-test-buster
+FROM docker.mgm.sipwise.com/sipwise-buster:latest
 
 # Important! Update this no-op ENV variable when this Dockerfile
 # is updated with the current date. It will force refresh of all
 # of the base images and things like `apt-get update` won't be using
 # old cached versions when the Dockerfile is built.
-ENV REFRESHED_AT 2021-08-11
+ENV REFRESHED_AT 2020-01-24
 
 RUN apt-get update && apt-get install --assume-yes --no-install-recommends \
   binutils \
@@ -13,7 +13,7 @@ RUN apt-get update && apt-get install --assume-yes --no-install-recommends \
   jenkins-debian-glue \
   libperl-critic-perl \
   parallel \
-  pycodestyle \
+  pep8 \
   ruby \
   shellcheck \
   xz-utils && \
@@ -43,12 +43,12 @@ WORKDIR /code/
 # (jump to the next section if you don't want to build yourself!):
 # NOTE: run the following command from root folder of git repository:
 #
-# % docker build --tag="jenkins-tap-test-bullseye" -f t/tap-tests-docker/Dockerfile .
-# % docker run --rm -i -t -v $(pwd):/code/source:rw jenkins-tap-test-bullseye:latest bash
+# % docker build --tag="jenkins-tap-test-buster" -f t/tap-tests-docker/Dockerfile .
+# % docker run --rm -i -t -v $(pwd):/code/source:rw jenkins-tap-test-buster:latest bash
 #
 # Use the existing docker image:
-# % docker pull docker.mgm.sipwise.com/jenkins-tap-test-bullseye
-# % docker run --rm -i -t -v $(pwd):/code/source:rw docker.mgm.sipwise.com/jenkins-tap-test-bullseye:latest bash
+# % docker pull docker.mgm.sipwise.com/jenkins-tap-test-buster
+# % docker run --rm -i -t -v $(pwd):/code/source:rw docker.mgm.sipwise.com/jenkins-tap-test-buster:latest bash
 #
 # Inside docker (the command is in history, just press UP button):
 #   LC_ALL=C.UTF-8 SHELL=bash WORKSPACE=/code/ /usr/bin/tap_tool_dispatcher