Fix issue with system_ready_for_rapid file

Fix issue with system_ready_for_rapid file

In the /opt/rapid directory, we used to check for the existance of the
file system_ready_for_rapid. This file was created when all the
initialization is done properly. This check was however broken and always
resulted succesfully, even if the file did not exist. When executing
runrapid.py, the system will now wait to connect to PROX, till this file
exists. The file is created when running start.sh

Signed-off-by: Luc Provoost <luc.provoost@gmail.com>
Change-Id: Idca52549aae40070a0b6ea1d7ccbf6c322dc631d