Update tests.yaml version to 2.4.0

Author: gmarz

src/Tests/tests.yaml

@@ -1,7 +1,7 @@
 # mode either u (unit test), i (integration test) or m (mixed mode)
-mode: u
+mode: m
 # the elasticsearch version that should be started
-elasticsearch_version: 2.3.5
+elasticsearch_version: 2.4.0
 # whether we want to forcefully reseed on the node, if you are starting the tests with a node already running
 force_reseed: true
 # do not spawn nodes as part of the test setup but rely on a manually started es node being up