Changes to the centos_6_x.sh bootstrap script:

* Changes REPO_URL to the latest 64 bit puppetlabs-release RPM (how was the i386 RPM tested on 64bit?)
* Tested on CentOS 6.5 x86_64
* Groups the if conditionals, cleaner this way
* Absolute paths for binaries
* rpm command installs the puppetlabs-release RPM directly, no need to wget it first
* Uses `quiet` options where available and removes /dev/null redirects