Jython leak : PyFile$Closer appended in a list which is never cleared

Jython leak : PyFile$Closer appended in a list which is never cleared. No use for vert.x to doing this, if closes are omitted, the JVM will close all the files at the end of its execution.

Simple verticle test to reproduce the issue :

* Set a lower heap space size
* Run :

```python
import vertx


while True:
	handler = open("test.txt", 'r')
	handler.readlines()
	handler.close()
```

* Wait few seconds / minutes :
=> Java Heap space OOM

Signed-off-by: Julien <jlehuraux@chyro.fr>