Revert "(FACT-451) Add Cumulus Linux distro to Debian OS family"

This partially reverts commit 919034f4de449bd56f60de6e7f748046aede76c0;
keeping the addition of the missing osfamily spec file.

The CumulusLinux distro detection isn't present in stable; backing out
the change to osfamily for CumulusLinux.
(FACT-466) Make kernelmajversion useful in FreeBSD

FreeBSD has used a 2-element release number since before 3.0. The
current kernalmajversion returns the first two elements of
kernelversion, which is exactly the same as kernelversion on FreeBSD.
This fact now returns just the first element when on FreeBSD.
Merge branch 'pr/629' into stable

* pr/629:
  (FACT-466) Make kernelmajversion useful in FreeBSD

Closes GH-629
(FACT-460) Modify $GEM_SOURCE for CI bootstrap

It is preferable to override the authoritative source (rubygems.org)
with our own internal resources, as opposed to the other way around.
This change ensures that if $GEM_SOURCE is set in the environment,
it is honored. Otherwise, we fall back to the public authority,
rubygems.org.

This change is analogous to the following line in our Gemfiles:

    source ENV['GEM_SOURCE'] || "https://rubygems.org"
Merge branch 'stable' into facter-2