Update for default configs

Update to allow for default config properties if some are not specified
with the start server and properties passed in.  Updated the tests to
match and also moved a few more things into the Constants.java file.

parser_commons/src/main/java/org/eclipse/moquette/commons/Constants.java

@@ -15,6 +15,8 @@
  */
 package org.eclipse.moquette.commons;
 
+import java.io.File;
+
 /**
  * Contains some useful constants.
  */
@@ -23,4 +25,7 @@ public class Constants {
     public static final int WEBSOCKET_PORT = 8080;
     public static final String HOST = "0.0.0.0";
     public static final int DEFAULT_CONNECT_TIMEOUT = 10;
+    public static final String DEFAULT_MOQUETTE_STORE_MAP_DB_FILENAME = "moquette_store.mapdb";
+    public static final String DEFAULT_PERSISTENT_PATH = System.getProperty("user.home") + File.separator + DEFAULT_MOQUETTE_STORE_MAP_DB_FILENAME;
+    public static final String PERSISTENT_STORE_PROPERTY_NAME = "persistence_store";
 }