Use container-based infrastructure (sudo: false) in TravisCI

.travis.yml

@@ -1,3 +1,4 @@
+sudo: false
 language: python
 python: 2.7
 os:
@@ -24,9 +25,13 @@ matrix:
   allow_failures:
   - env: TOX_ENV=py27-lint-imports
 
+addons:
+  apt:
+    packages:
+      - libxml2-utils
+
 install:
   - pip install tox
-  - if [ "$TOX_ENV" == "validate-test-tools" ]; then sudo apt-get install libxml2-utils; fi
   - if [ "$TOX_ENV" == "qunit" ]; then bash -c 'cd test/qunit && npm install'; fi
   - if [ "$TOX_ENV" == "first_startup" ]; then bash -c "bash scripts/common_startup.sh && wget -q https://github.com/jmchilton/galaxy-downloads/raw/master/db_gx_rev_0127.sqlite && mv db_gx_rev_0127.sqlite database/universe.sqlite && bash manage_db.sh -c ./config/galaxy.ini.sample upgrade"; fi