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/finit.c

@@ -602,7 +602,7 @@ static void bootstrap_worker(void *work)
 	 * Run startup scripts in the runparts directory, if any.
 	 */
 	if (runparts && fisdir(runparts) && !rescue)
-		run_parts(runparts, NULL, 1);
+		run_parts(runparts, NULL, NULL, 1);
 
 
 	/*