jenkins/mmc: added cleaning leftovers in perparing stage

Signed-off-by: Marc Mattmueller <marc.mattmueller@netmodule.com>

Jenkinsfile_mmcImages

@@ -20,7 +20,8 @@ pipeline {
   }
 
   environment {
-    IMG_OUTPUT_DIR = "tmp/build-output"
+    WORK_DIR = "tmp"
+    IMG_OUTPUT_DIR = "${WORK_DIR}/build-output"
   }
 
   options {
@@ -44,6 +45,8 @@ pipeline {
             error("Missing machine type --> select parameter MACHINE for a proper build")
           }
 
+          cleanLeftOvers(env.IMG_OUTPUT_DIR)
+
           // this definition is needed for selecting the
           // correct build directory
           env.BUILD_DIR_POSTFIX = ""
@@ -99,6 +102,7 @@ pipeline {
       post {
         always {
           script {
+            cleanLeftOvers(env.WORK_DIR)
             yoctocommon.syncSources("${env.DOWNLOAD_DIR}", "${env.BINARY_STORAGE_URL}")
           }
         }
@@ -135,6 +139,11 @@ def printJobParameters() {
 ----------------------------------\n"
 }
 
+//-----------------------------------------------------------------------------
+def cleanLeftOvers(cleaningDir) {
+  sh "rm -rf ${cleaningDir}"
+}
+
 //-----------------------------------------------------------------------------
 def build(imgType) {
   def tgtImgType = "${imgType}" == "bootloader" ? "dev" : "${imgType}"