Revert "TT#113650 Build 'buster' docker image"

Restoring back byllseye image for trunk. 'buster' one
was set temporary just in order to build missed docker image
for 'buster'

This reverts commit 94666c9714.

Change-Id: Ibb4f97d962987ddebdeee6fc38aadcb547af4b75

t/tap-tests-docker/Dockerfile

@@ -1,11 +1,11 @@
-# DOCKER_NAME=jenkins-tap-test-buster
-FROM docker.mgm.sipwise.com/sipwise-buster:latest
+# DOCKER_NAME=jenkins-tap-test-bullseye
+FROM docker.mgm.sipwise.com/sipwise-bullseye: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 2020-01-24
+ENV REFRESHED_AT 2021-08-11
 
 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 \
-  pep8 \
+  pycodestyle \
   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-buster" -f t/tap-tests-docker/Dockerfile .
-# % docker run --rm -i -t -v $(pwd):/code/source:rw jenkins-tap-test-buster:latest bash
+# % 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
 #
 # Use the existing docker image:
-# % 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
+# % 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
 #
 # 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