Add stage to clean workspace before beginning build

Change-Id: I8f928d9db3a122178dc54ecc3d75ec4f49685117
diff --git a/Jenkinsfile.release b/Jenkinsfile.release
index db3a89b..a76adaf 100644
--- a/Jenkinsfile.release
+++ b/Jenkinsfile.release
@@ -37,6 +37,10 @@
 }
 
 node ('master') {
+    stage ('Clean workspace') {
+        cleanWs()
+    }
+    
     stage ('Checkout code') {
         //checkout([$class: 'RepoScm', currentBranch: true, manifestRepositoryUrl: 'https://gerrit.opencord.org/manifest', quiet: true])
         git branch: branch, url: 'ssh://jenkins@gerrit.opencord.org:29418/' + app