Do we need trusty in Travis? (#3737)

* do we need trusty?

* add docker as a dependency for boulder??

.travis.yml

@@ -4,9 +4,6 @@ cache:
     directories:
         - $HOME/.cache/pip
 
-# This makes sure we get a host with docker-compose present.
-dist: trusty
-
 before_install:
   - 'dpkg -s libaugeas0'
 
@@ -21,30 +18,34 @@ matrix:
   include:
     - python: "2.7"
       env: TOXENV=cover BOULDER_INTEGRATION=1
-      sudo: true
+      sudo: required
       after_failure:
         - sudo cat /var/log/mysql/error.log
         - ps aux | grep mysql
+      services: docker
     - python: "2.7"
       env: TOXENV=lint
     - python: "2.7"
       env: TOXENV=py27-oldest BOULDER_INTEGRATION=1
-      sudo: true
+      sudo: required
       after_failure:
         - sudo cat /var/log/mysql/error.log
         - ps aux | grep mysql
+      services: docker
     - python: "2.6"
       env: TOXENV=py26 BOULDER_INTEGRATION=1
-      sudo: true
+      sudo: required
       after_failure:
         - sudo cat /var/log/mysql/error.log
         - ps aux | grep mysql
+      services: docker
     - python: "2.6"
       env: TOXENV=py26-oldest BOULDER_INTEGRATION=1
-      sudo: true
+      sudo: required
       after_failure:
         - sudo cat /var/log/mysql/error.log
         - ps aux | grep mysql
+      services: docker
     - sudo: required
       env: TOXENV=nginx_compat
       services: docker