DATAMONGO-1987 - Upgrade test infrastructure to MongoDB 4.0-rc0

Also make sure to use WriteConcern.MAJORITY when (re)creating collections in test setup.

.travis.yml

@@ -18,7 +18,7 @@ env:
   matrix:
     - PROFILE=ci
   global:
-    - MONGO_VERSION=3.7.9
+    - MONGO_VERSION=4.0.0-rc0
 
 addons:
   apt:

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/test/util/MongoTestUtils.java

@@ -44,7 +44,8 @@ public class MongoTestUtils {
 	public static MongoCollection<Document> createOrReplaceCollection(String dbName, String collectionName,
 			com.mongodb.MongoClient client) {
 
-		MongoDatabase database = client.getDatabase(dbName);
+		MongoDatabase database = client.getDatabase(dbName).withWriteConcern(WriteConcern.MAJORITY)
+				.withReadPreference(ReadPreference.primary());
 
 		boolean collectionExists = database.listCollections().filter(new Document("name", collectionName)).first() != null;