vnc: run websockify as background process

Instead of running as a daemon, making websockify run as a background
process. This ensures that the process gets cleaned up property if and
when job is terminated. With certain job schedulers/environments
(e.g. OpenPBS+AzHOP), this avoids dangling processes lingering post job
termination.

lib/ood_core/batch_connect/templates/vnc.rb

@@ -138,7 +138,7 @@ def after_script
               echo "Starting websocket server..."
               websocket=$(find_port)
               [ $? -eq 0 ] || clean_up 1 # give up if port not found
-              #{websockify_cmd} -D ${websocket} localhost:${port}
+              #{websockify_cmd} ${websocket} localhost:${port} &
 
               # Set up background process that scans the log file for successful
               # connections by users, and change the password after every