public static Version getPriorToServerVersion( Plugin plugin )
    {
        return getPriorToServerVersion( XMPPServer.getInstance().getPluginManager().getPluginPath( plugin ) );
    }
Returns the server version up, but not including, in which this plugin can run within. The value is retrieved from
the plugin.xml file of the plugin. If the value could not be found, {@code null} will be returned.

Note that this method will return data only for plugins that have successfully been installed. To obtain data
from plugin (directories) that have not (yet) been  installed, refer to the overloaded method that takes a Path
argument.

@param plugin The plugin (cannot be null)
@return the plugin's maximum server version (possibly null).
xmppserver/src/main/java/org/jivesoftware/openfire/container/PluginMetadataHelper.java