reproducible debian: Add a mean to very gracefully stop the rb workers

Signed-off-by: Mattia Rizzolo <mattia@debian.org>

bin/reproducible_worker.sh

 #!/bin/bash
+# vim: set noexpandtab:
 
 # Copyright © 2017 Holger Levsen (holger@layer-acht.org)
+#           © 2018 Mattia Rizolo <mattia@debian.org>
 # released under the GPLv=2
 
 set -e
@@ -41,6 +43,11 @@ while true ; do
 			break
 		fi
 	fi
+	LOCKFILE="/var/lib/jenkins/NO-RB-BUILDERS-PLEASE"
+	if [ -f "$LOCKFILE" ];
+		echo "The lockfile $LOCKFILE is present, thus stopping this"
+		break
+	fi
 
 	# sleep up to 2.3 seconds (additionally to the random sleep reproducible_build.sh does anyway)
 	/bin/sleep $(echo "scale=1 ; $(shuf -i 1-23 -n 1)/10" | bc )

hosts/jenkins/etc/systemd/system/reproducible_build@.service

 [Unit]
 Description=Build service for reproducible-builds jobs
+ConditionPathExists=!/var/lib/jenkins/NO-RB-BUILDERS-PLEASE
 
 [Service]
 # Restart whenever the script exits, without rate limiting: