TT#118659 Switch Dockerfile from Debian buster to bullseye

Change-Id: I9414891d240bc9192e01baf73e3da82d00aca5c6

t/Dockerfile

@@ -1,11 +1,11 @@
-# DOCKER_NAME=janus-admin-buster
-FROM docker.mgm.sipwise.com/sipwise-buster:latest
+# DOCKER_NAME=janus-admin-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 2021-04-05
+ENV REFRESHED_AT 2021-05-03
 
 COPY t/sources.list.d/builddeps.list /etc/apt/sources.list.d/
 COPY t/sources.list.d/preferences /etc/apt/preferences.d/
@@ -38,14 +38,14 @@ WORKDIR /code
 # (jump to the next section if you don't want to build yourself!).
 # The first you need to put the proper NGCP sources at t/sources.list.d/builddeps.list
 # for instance, trunk:
-# % echo "deb https://deb.sipwise.com/autobuild/ release-trunk-buster main" > t/sources.list.d/builddeps.list
-# % docker build --tag="janus-admin-buster" -f ./t/Dockerfile .
-# % docker run --rm -i -t -v $(pwd):/code:ro -v /results janus-admin-buster:latest bash
+# % echo "deb https://deb.sipwise.com/autobuild/ release-trunk-bullseye main" > t/sources.list.d/builddeps.list
+# % docker build --tag="janus-admin-bullseye" -f ./t/Dockerfile .
+# % docker run --rm -i -t -v $(pwd):/code:ro -v /results janus-admin-bullseye:latest bash
 #
 # Use the existing docker image:
-# % docker pull docker.mgm.sipwise.com/janus-admin-buster
+# % docker pull docker.mgm.sipwise.com/janus-admin-bullseye
 # NOTE: run the following command from root folder of git repository:
-# % docker run --rm -i -t -v $(pwd):/code:ro -v /results docker.mgm.sipwise.com/janus-admin-buster:latest bash
+# % docker run --rm -i -t -v $(pwd):/code:ro -v /results docker.mgm.sipwise.com/janus-admin-bullseye:latest bash
 #
 # Inside docker:
 #   cd /code && ./t/testrunner