Merge pull request #663 from perfectsense/bugfix/master-user-name-req…

…uired

Make Master user name required for DB cluster

src/main/java/gyro/aws/rds/DbClusterResource.java

@@ -394,6 +394,7 @@ public void setMasterUserPassword(String masterUserPassword) {
     /**
      * The name of the master user for the DB cluster.
      */
+    @Required
     public String getMasterUsername() {
         return masterUsername;
     }