Send a mail to bazel-ci@ with the report of the global post-submit

With that config the global post submit only send two mails at most
(and not a mail for every downstream job). And send one mail with
the actual report of A/B testing.

Change-Id: I1d514366f0e51648e04735db30bff0b5f622f6d4
diff --git a/jenkins/jobs/global.groovy b/jenkins/jobs/global.groovy
index 9429b04..0613fa2 100644
--- a/jenkins/jobs/global.groovy
+++ b/jenkins/jobs/global.groovy
@@ -109,4 +109,12 @@
 
 stage("Publish report") {
   reportAB report: report, name: "Downstream projects"
+  if (mail_recipient) {
+    mail(subject: "Global tests #${currentBuild.number} finished with status ${currentBuild.result}",
+         body: """A global tests has just finished with status ${currentBuild.result}.
+
+You can find the report at ${currentBuild.getAbsoluteUrl()}Downstream_projects/.
+""",
+         to: mail_recipient)
+  }
 }