abort previous builds (PegaSysEng#817)

Jenkinsfile

@@ -1,5 +1,9 @@
 #!/usr/bin/env groovy
 
+import hudson.model.Result
+import hudson.model.Run
+import jenkins.model.CauseOfInterruption.UserInterruption
+
 if (env.BRANCH_NAME == "master") {
     properties([
         buildDiscarder(
@@ -21,6 +25,26 @@ if (env.BRANCH_NAME == "master") {
 def docker_image = 'docker:18.06.0-ce-dind'
 def build_image = 'pegasyseng/pantheon-build:0.0.5-jdk11'
 
+def abortPreviousBuilds() {
+    Run previousBuild = currentBuild.rawBuild.getPreviousBuildInProgress()
+
+    while (previousBuild != null) {
+        if (previousBuild.isInProgress()) {
+            def executor = previousBuild.getExecutor()
+            if (executor != null) {
+                echo ">> Aborting older build #${previousBuild.number}"
+                executor.interrupt(Result.ABORTED, new UserInterruption(
+                    "Aborted by newer build #${currentBuild.number}"
+                ))
+            }
+        }
+
+        previousBuild = previousBuild.getPreviousBuildInProgress()
+    }
+}
+
+abortPreviousBuilds()
+
 try {
     parallel UnitTests: {
         def stage_name = "Unit tests node: "