Fix the copy-build-sshkey role

Run the first task in the block, with become_user since the zuul
user may not access a generic use .ssh folder.

Depends-on: https://review.openstack.org/550091

Change-Id: I4ce120412079fe92502eee5310a03664aa55d5ce

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

@@ -1,4 +1,6 @@
 ---
+# 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:
@@ -6,8 +8,6 @@
       manage_dir: yes
       key: "{{ lookup('file', zuul_temp_ssh_key ~ '.pub') }}"
 
-# Use a block to add become to a set of tasks
-- block:
   - name: Install the build private key
     copy:
       src: "{{ zuul_temp_ssh_key }}"