Trim whitespace from uri password for docker promote

The uri module faithfully passes the entire string, even if it has
trailing whitespace such as a newline. The zuul encrypt_secret
command currently does not trim, so if echo was used instead of
echo -n this can fail in a hard to debug manner.

Change-Id: Ic9525ac2925b6639f58604ca40dc878d20511ff8

roles/promote-docker-image/tasks/promote-retag.yaml

@@ -3,7 +3,7 @@
   uri:
     url: "https://auth.docker.io/token?service=registry.docker.io&scope=repository:{{ image.repository }}:pull,push"
     user: "{{ docker_credentials.username }}"
-    password: "{{ docker_credentials.password }}"
+    password: "{{ docker_credentials.password | trim }}"
     force_basic_auth: true
   register: token
 - name: Retag image