(FACT-698) Add fips_enabled fact

Adds a fips_enabled fact to determine if FIPS is enabled on the system.

FACT-698
It's possible that we have issues reading the proc file system on particular versions of Ruby that we would need to validate against supported Ruby versions:
https://github.com/puppetlabs/facter/blob/master/lib/facter/filesystems.rb#L24-L41