(FACT-603) Allow acceptance to use github mirror

This provides the necessary bits to allow facter to use github mirrors during
acceptance runs.
Merge branch 'ticket/stable/FACT-603-use-github-mirror' into stable

* ticket/stable/FACT-603-use-github-mirror:
  (FACT-603) Allow acceptance to use github mirror
Merge branch 'stable'

* stable:
  (FACT-603) Allow acceptance to use github mirror