(FACT-234) Partitions Fact

This fact adds a structured fact that reveals details of the partitions on the machine including things like UUID, size, mount point and filesystem.

This PR supersedes PR #560
Ive tried the tests with both 

      Facter.stubs(:value).with(:kernel).returns("SunOS")
      Facter.fact(:kernel).stubs(:value).returns("SunOS")

and altering Facter::Util::Partitions.implementation to suit to no avail...