Merge pull request #2755 from edx/feanil/apt_get_yes

Update to not receive input on apt-get tasks.

.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"