Update travis.yml to include more integration tests

Add tests against 6.6 snapshot (first Elasticsearch version to include
ILM) and update test against 7.0 to retrieve artifact, rather than
attempt to build master.

Author: robbavey

.travis.yml

@@ -9,8 +9,9 @@ env:
 - DISTRIBUTION=legacy INTEGRATION=true ES_VERSION=5.6.9 TEST_DEBUG=true
 - DISTRIBUTION=oss INTEGRATION=true ES_VERSION=6.4.3 TEST_DEBUG=true
 - DISTRIBUTION=default INTEGRATION=true ES_VERSION=6.4.3 TEST_DEBUG=true
-- DISTRIBUTION=default INTEGRATION=true ES_VERSION=6.x TEST_DEBUG=true
-- DISTRIBUTION=default INTEGRATION=true ES_VERSION=master TEST_DEBUG=true
+- DISTRIBUTION=oss INTEGRATION=true ES_VERSION=6.6.0-SNAPSHOT TEST_DEBUG=true
+- DISTRIBUTION=default INTEGRATION=true ES_VERSION=6.6.0-SNAPSHOT TEST_DEBUG=true
+- DISTRIBUTION=default INTEGRATION=true ES_VERSION=7.0.0-alpha1-SNAPSHOT TEST_DEBUG=true
 - DISTRIBUTION=legacyxpack SECURE_INTEGRATION=true INTEGRATION=true ES_VERSION=5.6.9 TEST_DEBUG=true
 - DISTRIBUTION=default SECURE_INTEGRATION=true INTEGRATION=true ES_VERSION=6.4.2 TEST_DEBUG=true
 
@@ -27,7 +28,7 @@ matrix:
   - rvm: jruby-1.7.27
     env: LOGSTASH_BRANCH=5.6
   allow_failures:
-  - env: DISTRIBUTION=default INTEGRATION=true ES_VERSION=master TEST_DEBUG=true
+  - env: DISTRIBUTION=default INTEGRATION=true ES_VERSION=7.0.0-alpha1-SNAPSHOT TEST_DEBUG=true
   fast_finish: true
 install: true
 script: ci/build.sh