public static String getDatabaseKey( Path pluginDir )
    {
        return getElementValue( pluginDir, "/plugin/databaseKey" );
    }
Returns the database schema key of a plugin, if it exists. The value is retrieved from the plugin.xml file of the
plugin. If the value could not be found, {@code null} will be returned.

@param pluginDir the path of the plugin directory.
@return the plugin's database schema key or {@code null} if it doesn't exist.
xmppserver/src/main/java/org/jivesoftware/openfire/container/PluginMetadataHelper.java