Bump deps and cleanup

[testeddoughnut]

• Bumped all deps to what the upstream plugins are using.
• Switch to using chefstyle so we don't have to managed our own rubocop config.
• Added support for most APIv4 options for Linode Create.
• Dropped some options (kernel, for example) that aren't supported on the create call.
• Added additional environment variable support for options where it made sense.
• Removed all the API calls to validate image, region, kernel etc since the create call does that for us.
• Added better error reporting for when the create call runs into trouble.
• Improved support for the post-build steps to set hostname and disable password login.
  • It now works for all base images that Linode offers, including the less popular ones.
  • It also now disables password login through SSH config instead of just locking the account.
• Added a .kitchen.yml file to test all base images. This is not added to the CI at this time.
• Updated all tests to be more comprehensive and to simulate the API calls with webmock.
• Filled out tests for some previous features I already added.