test/behat/mahara_behat.sh: Close Selenium after tests run

Leaving Selenium running has the advantage of quicker startup
times for tests, however it can cause hard to diagnose issues
when your are dealing with multiple projects using Selenium
(e.g. while also working with Moodle).

Change-Id: I3b1f99ff166fddb6ce04539a2fd9eeae9600de8a

test/behat/mahara_behat.sh

@@ -113,6 +113,10 @@ then
     echo "=================================================="
     echo
     echo "Shutdown"
+
+    # Kill Selenium
+    curl -o /dev/null --silent http://localhost:4444/selenium-server/driver/?cmd=shutDownSeleniumServer
+    # Kill PHP server
     kill $SERVER
 else
     # Help text if we got an unexpected (or empty) first param