OHAI-551

Add LXC guest hint, and unit test to virtualization.
OHAI-551

Add LXC notes, and full-content cgroup unit tests for LXC.

Change /proc/1/cgroup to /proc/self/cgroup, more consistent
with kernel documentation
[here](https://www.kernel.org/doc/Documentation/cgroups/).

Full-content examples of cgroups in OHAI-551 ticket
[here](https://tickets.opscode.com/browse/OHAI-551?focusedCommentId=47513&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-47513).
Add coverage for arbitrarily named cgroups

* Not all platforms may call a cgroup /lxc.
* For example, in the kernel documentation, 'Charlie' is used as an arbitrary cgroup name.
Add lxc host support

* Added regex anchors (^|$) for specificity.
* lxc hosts should match pattern: '<digit>:<subsystem:/' in /proc/self/cgroup
Change \w+ to .+, since cgroup names could include dashes
Check specifically for /lxc/ cgroup

* If cgroup is named lxc, with a container name (hex/alpha/digit/dashes), then its an lxc guest.
* If cgroup is named arbitrarily, then its not necessarily an lxc guest.
* If cgroup capabilities exist, and the cgroup is root (/), then its an lxc host.
Merge remote-tracking branch 'atomic-penguin/OHAI-551' into OHAI-182
update tests to work with LXC support