Update to not receive input on apt-get tasks.

Without the '-y' the tests stop to ask for input.

Keep the old config. Since it was edited by travis we probably
want that on instead of the default one.

.travis.yml

@@ -18,8 +18,8 @@ addons:
       - python-demjson
 
 before_install:
-  - sudo apt-get update
-  - sudo apt-get install docker-engine
+  - sudo apt-get -y update
+  - sudo apt-get -y install -o Dpkg::Options::="--force-confold" docker-engine
 
 install:
   - "pip install --allow-all-external -r requirements.txt"