Add test-backend from Zulip server.

Author: rht

.travis.yml

@@ -1,14 +1,30 @@
 language: python
+sudo: required
 python:
   - "2.7"
   - "3.4"
   - "3.5"
   - "3.6"
-env: TEST_SUITE=test-main
+env:
+  matrix:
+    - TEST_SUITE=test-main
+  global:
+    - BOTO_CONFIG=/tmp/nowhere
 matrix:
   include:
   - python: "3.6"
     env: TEST_SUITE=test-static-analysis
+  - python: "3.4"
+    env: TEST_SUITE=backend
+    script:
+    - cd
+    - git clone https://github.com/zulip/zulip.git
+    - cd zulip
+    - sed -i "s|[email protected]|python-zulip-api.git@pull/$TRAVIS_PULL_REQUEST|" requirements/common.txt
+    - ./tools/travis/setup-backend
+    - ./tools/travis/backend
+    addons:
+      postgresql: "9.3"
 install:
   - tools/provision
   - source zulip-api-py*-venv/bin/activate