Deploy ssh key as root for non-root users

The role to distribute the build ssh key to a user uses the "copy"
module in combination with become_user. When the target user is not
root, this does not work because the ansible user is not root
either and "copy" is not compatible with pipelining:
http://docs.ansible.com/ansible/latest/user_guide/become.html#becoming-an-unprivileged-user

To solve the issue run the copy as root and set the owner of the
target file. Use the "user" module to resolve "~" to the target user
home directory.

Change-Id: Ic66eb2b14bc55a412dfa73aa0722cd59887a4e83

roles/copy-build-sshkey/tasks/main.yaml

@@ -1,25 +1,36 @@
 ---
+# Add the authorization first, to take advantage of manage_dir
+- name: Authorize build key
+  authorized_key:
+    user: "{{ copy_sshkey_target_user }}"
+    manage_dir: yes
+    key: "{{ lookup('file', zuul_temp_ssh_key ~ '.pub') }}"
+  become: true
+  become_user: "{{ copy_sshkey_target_user }}"
+
 # Use a block to add become to a set of tasks
 - block:
-  # Add the authorization first, to take advantage of manage_dir
-  - name: Authorize build key
-    authorized_key:
-      user: "{{ copy_sshkey_target_user }}"
-      manage_dir: yes
-      key: "{{ lookup('file', zuul_temp_ssh_key ~ '.pub') }}"
+  - name: Get the {{ copy_sshkey_target_user }} user home folder
+    user:
+      name: "{{ copy_sshkey_target_user }}"
+    register: target_user_registered
 
+  # The copy module does not work with become_user even if pipelining is
+  # enabled when both ansible user and become_user are not root:
+  # http://docs.ansible.com/ansible/latest/user_guide/become.html#becoming-an-unprivileged-user
   - name: Install the build private key
     copy:
       src: "{{ zuul_temp_ssh_key }}"
-      dest: "~/.ssh/id_rsa"
+      dest: "{{ target_user_registered.home }}/.ssh/id_rsa"
       mode: 0600
+      owner: "{{ copy_sshkey_target_user }}"
       force: no
 
   - name: Install the build public key
     copy:
       src: "{{ zuul_temp_ssh_key }}.pub"
-      dest: "~/.ssh/id_rsa.pub"
+      dest: "{{ target_user_registered.home }}/.ssh/id_rsa.pub"
       mode: 0644
+      owner: "{{ copy_sshkey_target_user }}"
       force: no
   become: true
-  become_user: "{{ copy_sshkey_target_user }}"