CHEF-4259: Fix unpacking recipes with non-gnu tar

This probably isn't enough to handle every ancient version of tar, but
at least it fixes unpacking on SmartOS which is based on fairly recent
illumos.

There has been some discussion on CHEF-1201 to introduce a setting to configure a gnu compatible tar. I think the better solution is not to rely on GNU tar specific behaviour.

This could still be broken on older versions of tar that don't support decompression though, but it should work with most recent flavours.