introduce and use setfscreatecon_or_die

(patch by Yuichi Nakamura <ynakam@hitachisoft.jp>)
runcon: *yet another* fix for vda's brainfart :(

libbb/selinux_common.c

@@ -28,3 +28,13 @@ error:
 	context_free(con);
 	return NULL;
 }
+
+void setfscreatecon_or_die(security_context_t scontext)
+{
+	if (setfscreatecon(scontext) < 0) {
+		/* Can be NULL. All known printf implementations
+		 * display "(null)", "<null>" etc */
+		bb_perror_msg_and_die("cannot set default "
+				"file creation context to %s", scontext);
+	}
+}