Support ARM properly with withChownWorkspace

Author: mikedougherty

vars/withChownWorkspace.groovy

@@ -5,7 +5,12 @@ def call(Closure body=null) {
   } finally {
     try {
       echo "chowning workspace"
-      sh 'docker run --rm -v $(pwd):/workspace busybox chown -R "$(id -u):$(id -g)" /workspace'
+      def arch = sh(script: "docker version -f '{{ .Server.Arch }}'", returnStdout: true).trim()
+      def image = "busybox"
+      if (arch == "arm") {
+        image = "armhf/busybox"
+      }
+      sh "docker run --rm -v \$(pwd):/workspace ${image} chown -R \"\$(id -u):\$(id -g)\" /workspace"
     } catch (Exception e) {
       println e
     }