Tests don't pass if elasticsearch.yml does not contain azure discovery settings

For now, we remove forcing discovery settings with `discovery.type: azure`.
So a developer who wants to run this test needs to add it in his `elasticsearch.yml` file.

Due to #50
(cherry picked from commit 6ac4483)
(cherry picked from commit 1a80c4b)

src/test/java/org/elasticsearch/azure/itest/AzureSimpleITest.java

@@ -44,7 +44,9 @@ public class AzureSimpleITest extends AbstractAzureTest {
     protected Settings nodeSettings(int nodeOrdinal) {
         return ImmutableSettings.builder()
                 .put(super.nodeSettings(nodeOrdinal))
-                .put("discovery.type", "azure")
+                // For now we let the user who runs tests to define if he wants or not to run discovery tests
+                // by setting in elasticsearch.yml: discovery.type: azure
+                // .put("discovery.type", "azure")
                 .build();
     }