Upload build duration to splunk

test plan:
Go to splunk, search for events with event name
'jenkins.build.duration'

closes: CCI-360

flag = none

Change-Id: Iba607d434a40f77de92731ea3228cd768404461c
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/236220
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: James Butters <jbutters@instructure.com>
Reviewed-by: Rex Fleischer <rfleischer@instructure.com>
QA-Review: Jacob Powell <spowell@instructure.com>
Product-Review: Jacob Powell <spowell@instructure.com>

Jenkinsfile

@@ -442,6 +442,8 @@ pipeline {
           rspec.uploadSeleniumFailures()
           rspec.uploadRSpecFailures()
           load('build/new-jenkins/groovy/reports.groovy').sendFailureMessageIfPresent()
+          def splunk = load 'build/new-jenkins/groovy/splunk.groovy'
+          splunk.upload([splunk.event('jenkins.build.duration', ['duration': "$currentBuild.duration"])])
         }
       }
     }