Change the tarball template check

[dswd]

The current check tests whether the file ./sbin/init exists and belongs to 0/0. While the test itself is usefull, it can not be performed that way for several reasons:

1. Depending on how the tarball is created, the path can also be sbin/init.
2. Depending on how the tarball is created, the user can also be root/root.
3. Depending on the OS (e.g. Debian 9) /sbin is a symlink to /usr/sbin so there is no entry for /sbin/init.