Fix Debian compatibility

APT uses "amd64" instead of "x86_64" as the architecture label. Debian doesn't come with a `nobody` group, but uses `nogroup` instead. However, since the owner is `root`, I used the `root` group as well.

Gluster's repo is a little weird in that "wheezy" is hard-coded in the URL.
Yeah, I think I can manage that, for this change anyway. Fixing the repo isn't something I want to tackle at the moment.