Add templates for CentOS 5.10

New templates for CentOS 5.10 (x86_64/i386, ISO/netboot); loosely based on previous CentOS templates, but with the following changes and improvements:

- Updated Ruby to version 1.9.3-p484
- Chef installation via Opscode script
- Consolidated scripts; removed redundant/unused script parts
- Enabled Virtual Box Host IO Cache (Vagrant default setting)