lguest: fix lguest wake on guest clock tick, or fd activity

lguest: fix lguest wake on guest clock tick, or fd activity

The Launcher could be inside the Guest on another CPU; wake_up_process
will do nothing because it is "running".  kick_process will knock it
back into our kernel in this case, otherwise we'll miss it until the
next guest exit.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>