bifrost-configdrives-dynamic: automatically find ed25519 SSH keys

Also make the SSH key detection code a bit more readable.

Change-Id: Ia365f75d7fac3d64d8dce898ca854149c0aeed6e

playbooks/roles/bifrost-configdrives-dynamic/defaults/main.yml

@@ -6,7 +6,7 @@
 write_interfaces_file: false
 http_boot_folder: /httpboot
 # Default location to the ssh public key for the user operating Bifrost.
-ssh_public_key_path: "{{ lookup('env', 'HOME') }}/.ssh/id_rsa.pub"
+#ssh_public_key_path: "/path/to/id_rsa.pub"
 
 # Default interface name
 # TODO(TheJulia): Remove this default.

playbooks/roles/bifrost-configdrives-dynamic/tasks/ssh_public_key_path.yaml

@@ -12,18 +12,32 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 ---
-- name: "Defined ssh_public_key_path - Check to see if there is a file where the ssh_public_key_path is defined"
-  stat:
-    path: "{{ ssh_public_key_path }}"
-  register: test_ssh_public_key_path
-  when: ssh_public_key_path is defined
+- block:
+    - name: "Find a suitable SSH public key"
+      set_fact:
+        ssh_public_key_path: "{{ item }}"
+      with_first_found:
+        - "{{ lookup('env', 'HOME') }}/.ssh/id_rsa.pub"
+        - "{{ lookup('env', 'HOME') }}/.ssh/id_ed25519.pub"
+      when: ssh_public_key_path is undefined
+      ignore_errors: yes
+
+    - name: "Error if ssh_public_key_path cannot be detected"
+      fail:
+        msg: "ssh_public_key_path and cannot be guessed from ~/.ssh"
+      when: ssh_public_key_path is undefined
+
+    - name: "Check to see if there is a file where the ssh_public_key_path is defined"
+      stat:
+        path: "{{ ssh_public_key_path }}"
+      register: test_ssh_public_key_path
+
+    - name: "Error if ssh_public_key_path is not valid"
+      fail:
+        msg: "ssh_public_key_path {{ ssh_public_key_path }} was not found"
+      when: not test_ssh_public_key_path.stat.exists
   delegate_to: localhost
 
-- name: "Defined ssh_public_key_path - Error if ssh_public_key_path is not valid"
-  fail:
-    msg: "ssh_public_key_path is not valid."
-  when: not test_ssh_public_key_path.stat.exists
-  delegate_to: localhost
-
-- name: "Defined ssh_public_key_path - Read SSH public key in"
-  set_fact: ssh_public_key="{{ lookup('file', ssh_public_key_path ) }}"
+- name: "Read SSH public key in ssh_public_key"
+  set_fact:
+    ssh_public_key: "{{ lookup('file', ssh_public_key_path ) }}"