TT#113853 Preparations for release mr8.5.4, missing "mocha" binary

The job for unit test fails:

  20:48:18 + docker run --rm -i --entrypoint /bin/bash -v /var/lib/jenkins/workspace/janus-admin-unit-test-docker/source/:/code:ro -v /var/lib/jenkins/workspace/janus-admin-unit-test-docker/results:/results:rw docker.mgm.sipwise.com/janus-admin-buster:mr8.5.4 -c /code/t/testrunner
  20:48:28 ### Copying and moving files
  20:48:28 ################################################################################
  20:48:28 Finished main setup, now running tests ...
  20:48:29 npm WARN npm npm does not support Node.js v10.24.0
  20:48:29 npm WARN npm You should probably upgrade to a newer version of node as we
  20:48:29 npm WARN npm can't make any promises that npm will work with this version.
  20:48:29 npm WARN npm Supported releases of Node.js are the latest release of 4, 6, 7, 8, 9.
  20:48:29 npm WARN npm You can find the latest version at https://nodejs.org/
  20:48:29
  20:48:29 > janus-admin@1.0.5 test /tmp/code
  20:48:29 > mocha -b --exit -R spec --full-trace test/*-spec.js
  20:48:29
  20:48:29 sh: 1: mocha: not found
  20:48:29 npm ERR! Test failed.  See above for more details.

This dependency seems to be present in packages*.json package, however
it doesn't work.

So adding mocha as a pakcage to install, to try to get around the
problem and be able to build the package for the mr8.5.4 release.

Change-Id: I6c9bd2c2c1c9c17b7e2248cc26f3fcb134eb27ca
(cherry picked from commit 84eb9fc6e7)
(cherry picked from commit 20171b3e4a)

t/Dockerfile

@@ -5,7 +5,7 @@ FROM docker.mgm.sipwise.com/sipwise-buster: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 2019-08-05
+ENV REFRESHED_AT 2021-04-05
 
 COPY t/sources.list.d/builddeps.list /etc/apt/sources.list.d/
 COPY t/sources.list.d/preferences /etc/apt/preferences.d/
@@ -13,6 +13,7 @@ COPY t/sources.list.d/preferences /etc/apt/preferences.d/
 RUN apt-get update && \
   apt-get install --assume-yes \
         curl \
+        mocha \
         nodejs \
         npm \
         && \