Handle daemonization of pcid in a better way

Currently pcid exits the main thread once it is done spawning drivers and expects all background threads handling driver communication to stay around. This only works as exitting the main thread on redox os currently doesn't cause the whole process to die. This will have to be fixed at some point for compatibility with programs that expect that exitting the main thread kills all other threads in the process, at which point pcid would break without the changes in this commit.