Add in packer image example improvements

[iataylor]

Overview : After implementing and experimenting with the runners for my whole company, I've happened upon quite a few improvements to the default images. I'd like to propose adding them to the project, but I'll need permission to open a branch first.

Items :

• Winrm provisioner is slow, so I set up an ssh provisioner by default instead, which almost halves our build time once we have multiple provisioner scripts.
• For any practical use of the Windows runners, the default storage space (I think it's 30 gigs) is way too small. Updating the default images' volume size to 100 gigs is a much more reasonable size.
• Improvements in the chocolatey install that takes less time, and ensures the path is set at startup.

[npalm]

@iataylor improved examples would be very welcome. But no need to have permissions on this repository. You simply fork this repository. Make the changes on the fork (or an branch in the fork). Next you open a PR back to this repository to contibute back. Looking forward to your PR (pull request).

[iataylor]

#4258