(FACT-3154) Updates File.exist? method
(FACT-3154) Updates File.exist? method

The File.exists? method was deprecated in Ruby 2.1.0:
https://github.com/ruby/ruby/blob/6d728bdae9de565ad9d0b2fee2d4c2a33c6f4eac/file.c#L1414

And removed entirely from 3.2.0 onward:
https://bugs.ruby-lang.org/issues/17391

This commit updates that method to File.exist? in the directory
loader spec tests.

puppetlabs/facter,puppetlabs/facter,puppetlabs/facter