Support for Red Hat based systems when /etc/issue does not contain distro information
Added a note about having to opt-in to the new CentOS AMI
Update Debian 7 integration test AMI

Use Debian provided Debian Wheezy 7.0.0 EBS AMI.

[ci skip]
Update the Debian 7.0 AMI again

The image was rebuilt.
Add a helper to run commands with fallbacks
Default to `lsb_release` for detecting the Linux distro

/etc/issues is very unreliable as it is often modified by providers.
Merge pull request #242 from tmatilai/prefer-lsb_release

Default to `lsb_release` for detecting the Linux distro and add support
for RHEL based systems where /etc/issue is modified.

Fixes #234 too.
Update changelog

[ci skip]