Vagrant has been failing to run on CentOS 6 since version 1.2.5.
The read of file /etc/redhat-release appeared to be only checking for the word Fedora. Altered the regex to match CentOS as well
The version_number regex was causing an error because my /etc/redhat-release looks like this:
Fedora Core release 6 (Zod)
This fix allowed initialize to run just fine on my ridiculously old release.