Delete files in dest that don't exist

When using static nodes, we don't properly delete stale files nolonger
tracked in git.

Change-Id: Icb3b140abd1e2e3f1ca127f91f78c0df7efc4298
Signed-off-by: Paul Belanger <pabelanger@redhat.com>

roles/prepare-workspace/tasks/main.yaml

@@ -1,9 +1,10 @@
-# TODO(pabelanger): Handle cleanup on static nodes
 - name: Start zuul_console daemon.
   zuul_console:
 
 - name: Synchronize src repos to workspace directory.
   synchronize:
+    delete: true
     dest: "{{ zuul_workspace_root }}"
+    recursive: true
     src: "{{ zuul.executor.src_root }}"
   no_log: true