Fix empty include in configuration

An empty 'include' configuration would produce a beanScrope of '*:*' and
would match every bean from the server without applying any of the
default configuration

src/main/java/org/datadog/jmxfetch/Configuration.java

@@ -43,7 +43,7 @@ public String toString() {
     }
 
     private Boolean hasInclude() {
-        return getInclude() != null;
+        return getInclude() != null && !getInclude().isEmptyFilter();
     }
 
     /**

src/main/java/org/datadog/jmxfetch/Filter.java

@@ -188,4 +188,8 @@ public List<String> getParameterValues(String parameterName) {
     public boolean isEmptyBeanName() {
         return (filter.get("bean") == null && filter.get("bean_name") == null);
     }
+
+    public boolean isEmptyFilter() {
+        return filter.isEmpty();
+    }
 }