Various cleanup

@jerryk55 Please review.

I was also going to add a rescue around the `require 'ffi-vix_disk_lib'` in spec_helper.rb with a note that the user has to install the VixDiskLib in order to run the specs, and it can't be redistributed by the gem itself.  On that note, can we even run any specs on Travis?  Can we install the VixDiskLib automatically on Travis? /cc @roliveri