fix chocolatey latest logic

The current chocolatey-update behavior states that if a package
is not installed, then chocolatey returns "nothing to update"

This commit, adjusts the ensure=>latest logic: specifically

Case: Package is not installed
Action: Provider will perform a chocolatey install
Result: the latest package installed

Case: Package is installed but oldIf
Action: Provider will run chocolatey update to the latest version
Result: the latest package installed

Case: Package is already on the latest version
Action: Provider will not do anything.
Result: the latest packaged installed

This also clarified variable name from latest method
packages is really package_ver