Set correct initial bootstrap runlevel 'S'

This patch corrects a long standing issue with Finit.  System initial
bootstrap runlevel must be set to 'S' (0), not the configured fallback
runlevel 'RUNLEVEL', which likely is '2'.

Also, minor cleanup, reduce code duplication.

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

helpers.c

@@ -49,6 +49,7 @@ void runlevel_set(int pre, int now)
 {
 	struct utmp utent;
 
+	memset(&utent, 0, sizeof(utent));
 	utent.ut_type  = RUN_LVL;
 	utent.ut_pid   = (encode(pre) << 8) | (encode(now) & 0xFF);
 	strlcpy(utent.ut_user, "runlevel", sizeof(utent.ut_user));