add triggers based on cron

Signed-off-by: Héctor Orón Martínez <hector.oron@collabora.co.uk>
Reviewed-by: Andrew Shadura <andrew.shadura@collabora.co.uk>
Reviewed-by: Denis Pynkin <denis.pynkin@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D7264

Jenkinsfile

 release = "17.12"
 
+properties(
+    [
+        pipelineTriggers([cron('H H(1-4) * * *')]),
+    ]
+)
+
 def buildImage(architecture, type, board, debosarguments = "") {
   return {
     node("docker-slave") {