Rely on vagrant-core GracefulHalt for action_halt, and use action_halt in action_destroy
Don't call action_halt in destroy, as it disconnects from the datacenter handle
Merge branch 'master' into clintoncwolfe-shutdown-guest-on-halt
Update specs for graceful halt.

- test for GracefulHalt action instead of PowerOff

- update stubs to work with the GracefulHalt action
Merge branch 'clintoncwolfe-shutdown-guest-on-halt'

[Resolves GH-103]