Add CentOS 6.4 minimal templates.

Based on the 6.3 x64_86 minimal template with a couple minor changes:

- Install chef via the new omnibus installer (so the ruby definitions
are no longer explicitly needed).
- Update the ks.cfg "%packages" to match the defaults from a standard
CentOS 6.4 minimal install.
Merge pull request #588 from GUI/master

Add CentOS 6.4 minimal templates