Add actions for pausing/suspending (and inverse).

These actions are all already supported by the Fog library. They perform
the following actions to a compute machine:

* Pause/Unpause will stop a running virtual machine and keep the VM in
  memory on the hardware;

* Suspend/unsuspend will stop a running VM and write its contents to disk;
Merge pull request #33 from johnbellone/master

Add actions for pausing/suspending/halt/reload.