Use sha256 instead of md5 by default

Change-Id: I8564228e221919829541124c36baae60a874f1e5

doc/source/user/howto.rst

@@ -141,7 +141,7 @@ in an ``instance_info`` variable, for example:
         },
         "instance_info": {
           "image_source": "http://image.server/image.qcow2",
-          "image_checksum": "<md5 checksum>",
+          "image_checksum": "<md5/sha256/sha512 checksum>",
           "configdrive": {
             "meta_data": {
               "public_keys": {"0": "ssh-rsa ..."},

playbooks/roles/bifrost-deploy-nodes-dynamic/tasks/main.yml

@@ -82,7 +82,7 @@
           stat:
             path: "{{ deploy_image_path }}"
             get_checksum: yes
-            checksum_algorithm: md5
+            checksum_algorithm: sha256
           register: test_deploy_image
           become: yes
 

playbooks/roles/bifrost-ironic-install/tasks/bootstrap.yml

@@ -423,7 +423,7 @@
 - when: download_custom_deploy_image | bool
   block:
     - name: "Create a checksum file for the custom deployment image"
-      shell: md5sum {{ deploy_image_filename }} > {{ deploy_image_filename }}.CHECKSUMS
+      shell: sha256sum {{ deploy_image_filename }} > {{ deploy_image_filename }}.CHECKSUMS
       args:
         chdir: "{{ http_boot_folder }}"
     - name: "Ensure the checksum file is readable"

releasenotes/notes/no-md5-38bb5be4da0f8d4a.yaml

@@ -0,0 +1,4 @@
+---
+upgrade:
+  - |
+    SHA256 is now used instead of MD5 for any checksums calculated by Bifrost.