contrib/ci: add build dependency versioning (#1915)

contrib/ci/Jenkinsfile

@@ -15,7 +15,7 @@ pipeline {
 					}
 				}
 				stage('lint-sh') {
-					agent { label 'gluon-docker' }
+					agent { label 'gluon-docker-v1' }
 					steps {
 						sh 'make lint-sh'
 					}
@@ -38,3 +38,13 @@ pipeline {
 		}
 	}
 }
+
+# api-history:
+#
+# Every time the build dependencies of gluon change, the version
+# every container has to be rebuilt. Therefore, we use Jenkins
+# labels which intoduce a version number which is documented here.
+# As soon, as you properly rebuilt your docker container, you
+# can notify lemoer, that you have updated your node.
+#
+# - gluon-docker-v1: add shellcheck binary to the build environment

contrib/ci/jenkins-community-slave/README.md

@@ -26,7 +26,7 @@ docker run --detach --restart always \
    - Your node should appear [here](https://build.ffh.zone/label/gluon-docker/).
    - When clicking on it, Jenkins should state "Agent is connected." like here: 
 ![Screenshot from 2019-09-24 01-00-52](https://user-images.githubusercontent.com/601153/65469209-dac6c180-de66-11e9-9d62-0d1c3b6b940b.png)
-5. **Your docker container needs to be rebuilt, when the build dependencies of gluon change. So please be aware of that and update your docker container in that case.** 
+5. **Your docker container needs to be rebuilt, when the build dependencies of gluon change. As soon as build dependencies have changed, the build dependency api level has to be raised.** After you rebuilt your docker container, notifiy @lemoer, so he can bump the versioning number.
 
 ## Backoff
 - If @lemoer is not reachable, please be patient at first if possible. Otherwise contact info@hannover.freifunk.net or join the channel `#freifunkh` on hackint.