Use elasticsearch via docker, so that we can test against ES 1.5.2

.travis.yml

 language: python
+
 python:
     - "3.5"
+
+services:
+  - docker
+
 sudo: false
 
 # Cache the pip directory. "cache: pip" doesn't work due to install override. See https://github.com/travis-ci/travis-ci/issues/3239.
 cache:
   - directories:
     - $HOME/.cache/pip
+
 before_install:
     - "export DISPLAY=:99.0"
     - "sh -e /etc/init.d/xvfb start"
+    - docker run --detach  --publish 9200:9200 --publish 9300:9300 elasticsearch:1.5.2
+
 install:
     - pip install -U pip wheel codecov
     - pip install -r requirements/test.txt
+
+before_script:
+# Give Elasticsearch time to start
+  - sleep 10
+
 script:
     - make validate
-branches:
-    only:
-        - master
+
 after_success:
     - codecov

course_discovery/settings/test.py

 import os
-
 from course_discovery.settings.base import *
 
-
 # TEST SETTINGS
 INSTALLED_APPS += (
     'django_nose',
@@ -31,3 +29,9 @@ DATABASES = {
     },
 }
 # END IN-MEMORY TEST DATABASE
+
+ELASTICSEARCH = {
+    'host': os.environ.get('TEST_ELASTICSEARCH_HOST', 'localhost'),
+    'index': 'course_discovery_test',
+    'connect_on_startup': True
+}

docker-compose.yml

@@ -34,6 +34,8 @@ course-discovery:
   volumes:
     - .:/edx/app/course_discovery/course_discovery
   command: /edx/app/course_discovery/devstack.sh start
+  environment:
+    TEST_ELASTICSEARCH_HOST: "es"
   ports:
     - "18381:18381"
     - "8381:8381"