Make sure authorized_keys is not altered during a job

Change-Id: I5086fc7004c24813e4dae5a4c12037f237502d27

playbooks/base/cleanup.yaml

@@ -1,3 +1,8 @@
 - hosts: all
   roles:
     - remove-build-sshkey
+  tasks:
+    - name: Reinstall saved authorized_keys
+      copy:
+        src: "{{ zuul.executor.work_root }}/{{ inventory_hostname }}_authorized_keys"
+        dest: "{{ ansible_user_dir }}/.ssh/authorized_keys"

playbooks/base/pre.yaml

@@ -1,4 +1,9 @@
 - hosts: all
+  pre_tasks:
+    - name: Save authorized_keys
+      fetch:
+        src: "{{ ansible_user_dir }}/.ssh/authorized_keys"
+        dest: "{{ zuul.executor.work_root }}/{{ inventory_hostname }}_authorized_keys"
   roles:
     - add-build-sshkey
     - prepare-workspace