Travis add python-lvm2 dependency

.travis.yml

@@ -3,6 +3,9 @@ dist: trusty
 language: python
 python:
   - '2.7'
+before_install:
+  - sudo apt-get -qq update
+  - sudo apt-get install -y python-lvm2
 install:
   - pip install --quiet -r ci/requirements.txt
   - git clone https://github.com/"${TRAVIS_REPO_SLUG%%/*}"/qubes-builder ~/qubes-builder