This patch implements the start, stop and reboot methods for the Server
model instances.
These server model methods share common names with the AWS server model.
This patch also implements the API requests required to control the
power state of a VMware Virtual Machine.
The requests default to issuing shutdown and reboot commands to the
guest operating system itself. However, if force is set to true for
power_off and reboot, then the VM is powered off or reset at the virtual
hardware layer.
