Custom node shutdown after n number of runs

Node shutdown works fine, just the decrement counter fails to work. I will take one of the mac nodes on the current grid and test with. 

After getting the code, compile with:
```
./go selenium-server-standalone
```
Launch the hub and node with:
```
java -jar build/java/server/src/org/openqa/grid/selenium/selenium-standalone.jar -role hub

java -jar build/java/server/src/org/openqa/grid/selenium/selenium-standalone.jar -role node -hub http://localhost:4444/grid/register -nodeConfig node_config.txt -servlets org.openqa.grid.selenium.utils.NodeShutDownServlet
```

Here is the code snippet I tested with
```
from selenium import webdriver

hub_host = 'localhost'
hub_port = '5555'

command_executor = 'http://%s:%s/wd/hub' % (hub_host, hub_port)
dc = webdriver.DesiredCapabilities.FIREFOX.copy()

driver = webdriver.Remote(
	command_executor=command_executor,
	desired_capabilities=dc
)

driver.get("http://www.google.com")
driver.quit()
```