Integrate usr.sbin/nmtree/tests from NetBSD into atf/kyua

In collaboration with: pho
Sponsored by: EMC / Isilon Storage Division
Set the autoindent to 4 spaces with vim in BSD.tests.dist

This will prevent vim users from accidentally checking in buggy mtree files
(mixed tabs/spaces).

MFC after: 2 weeks
Sponsored by: EMC / Isilon Storage Division