race condition in download role under vagrant

using a shared folder can cause race conditions for the download
role as it tries to download files on all the nodes to the same
shared path.  This adds a flag to run the tasks in the download
role on just one node.

roles/download/defaults/main.yml

@@ -1,6 +1,9 @@
 ---
 local_release_dir: /tmp
 
+# if this is set to true will only download files once
+download_run_once: False
+
 # Versions
 kube_version: "v1.2.4"
 etcd_version: v2.2.5

roles/download/tasks/main.yml

@@ -2,6 +2,7 @@
 - name: Create dest directories
   file: path={{local_release_dir}}/{{item.dest|dirname}} state=directory recurse=yes
   with_items: "{{ downloads }}"
+  run_once: "{{ download_run_once|bool }}"
 
 - name: Download items
   get_url:
@@ -11,6 +12,7 @@
     owner: "{{ item.owner|default(omit) }}"
     mode: "{{ item.mode|default(omit) }}"
   with_items: "{{ downloads }}"
+  run_once: "{{ download_run_once|bool }}"
 
 - name: Extract archives
   unarchive:
@@ -21,6 +23,7 @@
     copy: no
   when: "{{item.unarchive is defined and item.unarchive == True}}"
   with_items: "{{ downloads }}"
+  run_once: "{{ download_run_once|bool }}"
 
 - name: Fix permissions
   file:
@@ -30,3 +33,4 @@
     mode: "{{ item.mode|default(omit) }}"
   when: "{{item.unarchive is not defined or item.unarchive == False}}"
   with_items: "{{ downloads }}"
+  run_once: "{{ download_run_once|bool }}"