Fix unrecognized option "p" in busybox ps

utils/novnc_proxy

@@ -193,7 +193,7 @@ echo "Starting webserver and WebSockets proxy on port ${PORT}"
 ${WEBSOCKIFY} ${SYSLOG_ARG} ${SSLONLY} --web ${WEB} ${CERT:+--cert ${CERT}} ${KEY:+--key ${KEY}} ${PORT} ${VNC_DEST} ${HEARTBEAT_ARG} ${IDLETIMEOUT_ARG} ${RECORD_ARG} ${TIMEOUT_ARG} ${WEBAUTH_ARG} ${AUTHPLUGIN_ARG} ${AUTHSOURCE_ARG} &
 proxy_pid="$!"
 sleep 1
-if ! ps -p ${proxy_pid} >/dev/null; then
+if [ -z "$proxy_pid" ] || ! ps -eo pid= | grep -w "$proxy_pid" > /dev/null; then
     proxy_pid=
     echo "Failed to start WebSockets proxy"
     exit 1