Domain type 'kvm' should be configurable and use qemu:/// uri.

Previous versions simply defaulted to 'kvm'. Now that they default to
'qemu', there is typically a 5x performance decrease that makes vagrant
unusably slow.
Merge pull request #182 from purpleidea/kvm-fix

Domain type 'kvm' should be configurable and use qemu:/// uri.
Support for adding additional disks through the Vagrantfile.

This patch lets you define multiple additional disks in your
Vagrantfile.
Include changes recommended by patch review for multiple disks.
Merge pull request #178 from purpleidea/feat/disks

Support for adding additional disks through the Vagrantfile.
Typo fix + punctuation consistency adjustments
Merge pull request #183 from justinclift/master

Typo fix + punctuation consistency adjustments