Fix stat check for add-build-sshkey

We incorrectly include create-key-and-replace.yaml based on the ssh
key existing.

Change-Id: Ia7b0c1338e7d746818bda579a82fdb6d74f81c31
Signed-off-by: Paul Belanger <pabelanger@redhat.com>

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

@@ -7,4 +7,5 @@
 
 - name: Create a new key in workspace based on build UUID
   include: create-key-and-replace.yaml
-  when: zuul_temp_ssh_key_stat is defined
+  when:
+    - zuul_temp_ssh_key_stat.stat.exists != True