(PA 1924) Updates to puppet-agent paths for Puppet 6

[caseywilliams]

There are two commits here:

• The first creates a new, separate section in file_paths.md for Puppet 6, where mcollective is removed and vendor_modules is added (these changes have already been made in the puppet-agent repo).
• The second updates the Windows paths used for Puppet 6 so that they more closely match their *nix counterparts (this work has not been done yet but will start very soon). Summary of changes:
  • The structure of C:\ProgramData has been left alone.
  • The ruby installation has moved from its own subdirectory (sys/ruby) to the same prefix used by other components.
  • Ditto for items in sys/tools
  • The components hiera, puppet, and pxp-agent also move from their own eponymous directories to the usual prefix.

[caseywilliams]

I've updated this PR to reflect the structure that has taken shape in https://github.com/puppetlabs/puppet-agent/pull/1517 -- agents with these new paths are passing integration tests now, but upgrade testing still remains before we can merge the changes.

[glennsarti]

I'd also like to see this line removed as part of this PR.

C:\Windows\Temp # :module_working_dir

That should probably be TEMP environment variable

[caseywilliams]

Thanks @glennsarti! I've pushed some updates that I hope cover the comments so far