Remove trailing newline from docker options

This is so that a long line can be broken using YAML line continuation
syntax, e.g.:

  docker_opts: >
    -H unix:https://
    -H IP:PORT
    --tls
    --tlscacert=...

(if not stripped, the newline will end up within the double-quotes)

tasks/main.yml

@@ -73,7 +73,7 @@
 
 - name: Set docker daemon options
  copy:
- content: "DOCKER_OPTS=\"{{ docker_opts }}\""
+ content: "DOCKER_OPTS=\"{{ docker_opts.rstrip('\n') }}\""
  dest: /etc/default/docker
  owner: root
  group: root