Fix #315: add environment variables to hook scripts

All hook scripts are called with at least one environment variable set,
FINIT_HOOK_NAME, useful when reusing the same hook script for multiple
hook points.  It is set to the string name, also used by the path, e.g.,
hook/net/up.

For all hook points from hook/sys/shutdown and later, FINIT_SHUTDOWN is
also set, to one of:  halt, poweroff, reboot.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/sig.c

@@ -302,6 +302,7 @@ void do_shutdown(shutop_t op)
 		sched_setscheduler(1, SCHED_RR, &sched_param);
 	}
 
+	halt = op;
 	if (sdown)
 		run_interactive(sdown, "Calling shutdown hook: %s", sdown);