CASSJAVA-131: Add Retention Requirement to Jenkinsfile-asf
patch by Jane He; reviewed by Michael Semb Wever

Jenkinsfile-asf

diff --git a/Jenkinsfile-asf b/Jenkinsfile-asf
index 4b50419..0abeb43 100644
--- a/Jenkinsfile-asf
+++ b/Jenkinsfile-asf
@@ -29,6 +29,10 @@
         cron(branchPatternCron().matcher(env.BRANCH_NAME).matches() ? '@weekly' : '')
     }
 
+    options {
+        buildDiscarder(logRotator(daysToKeepStr: '60', numToKeepStr: '30'))
+    }
+
     stages {
         stage('Matrix') {
             matrix {