Add support for detecting release version on CentOS 5 and CentOS 6

[irasnyd]

This is implemented by parsing the /etc/redhat-release file, looking for
the first instance of any two numbers separated by a '.' character. This
has held true for all versions of CentOS 5 and 6.

Examples of /etc/redhat-release from both versions:
CentOS release 5.11 (Final)
CentOS release 6.7 (Final)

[trustin]

@irasnyd Sorry for a late reply. Could your modification also be applied for RHEL and Fedora? If so, could you update your PR so that it also detects RHEL, Fedora, and potentially other distributions?

[irasnyd]

From my experience with CentOS, just matching the first number in /etc/redhat-release is sufficient to retrieve the distro major version number. The URL below shows that this will work for Fedora also. (I use CentOS exclusively, so I cannot test on RHEL or Fedora.)

http://www.putorius.net/2012/09/how-to-find-which-version-of-red-hat-is.html

I moved the version detection outside of the if statement, as it now applies to all of the older distros which use the /etc/redhat-release file. I also added a new regex which just matches a single number, since the VERSION_REGEX matches two numbers separated by a dot. This is so that Fedora will work (Fedora does not have sub-versions).

[trustin]

Thanks for a quick update! LGTM.

@nmittler, wanna take a look as well?

[nmittler]

LGTM ... thanks @irasnyd :)