(refactor) Use braces for one line blocks
(refactor) Deduplicate operatingsystem fact resolution

The operatingsystem fact on Linux had all possible fact resolutions
expressed in a single location. This makes testing and reasoning about
the fact somewhat frail, as it implies ordering that might or might not
be there.

This commit extracts common behavior of detecting redhat and suse
variants based on file contents, and behavior around detecting the
operating system based on the presence of a file.
(maint) disambiguate SLC and Scientific linux regexes

The regexes to detect Scientific Linux and Scientific Linux CERN were
ambiguous and order dependent. Since the regexes were stored in a hash
and were thus unordered, these looser regexes could cause mismatches.

This commit uses stricter regexes for both SL and SLC to disambiguate
this.
Merge pull request #494 from adrienthebo/refactor-operatingsystem

Refactor operatingsystem fact structure