[PATCH] cleanup udevstart

[PATCH] cleanup udevstart

I just wanted to terminate the snprintf() strings, cause I can see a
overflow with closed eyes after all the audit :)

But then I changed a bit more to bring it in line with the style of the
other files. I replaced the exec_udev() function with the one from
udevd, cause we don't need to read the stdout from udev.

Please have a look if it still works for you too and not
only for usernames with 3 characters :)