Add Puppet as a supported CentOS provisioner

Debian support is pending, but CentOS is a good start.
Also updated comments in provisioner.sh, in preparation for standardizing
other shell provisioner scripts.
Remove use of Perl from CentOS provisioner script

Replaced with a small shell pipeline instead.
Merge branch 'puppetize' of https://github.com/mckern/basebox-packer into mckern-puppetize
Reformatting to match recent changes in the Mac OS X scripts and upcoming script changes for all the boxes