TT#60100 TT#44859 Update janus-admin Dockerfile (as we mark it as 'upstream')

It was never build before, we have just recently started handling
this repository as 'upstream' and build it per git branch, see TT#44859.

Previous Jenkins was not able to build it:
> The following packages have unmet dependencies:
>  nodejs : Conflicts: nodejs-legacy
>           Conflicts: npm
Removing unnecessary dependencies.

Change-Id: I754a382e506fb8ffff7db37ec534a8966262cb28

t/Dockerfile

@@ -5,17 +5,17 @@ FROM docker.mgm.sipwise.com/sipwise-stretch:latest
 # 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 2017-09-25
+ENV REFRESHED_AT 2019-07-02
 
-# TODO - the release-trunk-stretch is too dynamic yet, though required build deps
-RUN echo "deb https://deb.sipwise.com/autobuild/ release-trunk-stretch main" >>/etc/apt/sources.list
+COPY t/sources.list.d/builddeps.list /etc/apt/sources.list.d/
+COPY t/sources.list.d/preferences /etc/apt/preferences.d/
 
-RUN apt-get update
-RUN apt-get install --assume-yes \
+RUN apt-get update && \
+  apt-get install --assume-yes \
         curl \
         nodejs \
-        nodejs-legacy \
-        npm
+        && \
+  apt-get clean
 
 ADD package.json /tmp/
 ADD npm-shrinkwrap.json /tmp/
@@ -30,10 +30,13 @@ RUN echo "cd /code && ./t/testrunner" >/root/.bash_history
 WORKDIR /code
 
 ################################################################################
-# Instructions for usage
+# Instructions for usage (from root folder of git repository)
 # ----------------------
-# When you want to build the base image from scratch (jump to the next section if you don't want to build yourself!):
-# NOTE: run the following commands from root folder of git repository:
+# When you want to build the base image from scratch
+# (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-stretch" -f ./t/Dockerfile .
 # % docker run --rm -i -t -v $(pwd):/code:ro -v /results janus-admin-stretch:latest bash
 #