WIP for #196

Adds some of the plugins. Need to check that we have all the ones we
need.

docs/ci/jenkins/docker/Dockerfile

@@ -0,0 +1,3 @@
+FROM jenkins/jenkins:lts
+COPY plugins.txt /usr/share/jenkins/ref/plugins.txt
+RUN /usr/local/bin/install-plugins.sh < /usr/share/jenkins/ref/plugins.txt

docs/ci/jenkins/docker/plugins.txt

@@ -0,0 +1,36 @@
+active-directory:latest
+antisamy-markup-formatter:latest
+build-name-setter:latest
+build-pipeline-plugin:latest
+build-timeout:latest
+cloudbees-folder:latest
+conditional-buildstep:latest
+config-file-provider:latest
+copyartifact:latest
+credentials:latest
+credentials-binding:latest
+dashboard-view:latest
+email-ext:latest
+embeddable-build-status:latest
+git-parameter:latest
+git:latest
+github-branch-source:latest
+github:latest
+gitlab-plugin:latest
+jenkins-multijob-plugin:latest
+junit:latest
+lockable-resources:latest
+mailer:latest
+matrix-auth:latest
+parameterized-trigger:latest
+pipeline-github-lib:latest
+pipeline-stage-view:latest
+rebuild:latest
+role-strategy:latest
+ssh-agent:latest
+throttle-concurrents:latest
+timestamper:latest
+warnings:latest
+workflow-aggregator:latest
+ws-cleanup:latest
+xunit:latest