[product: zaphod][project: zaphod-v0.3]: [bug]Add time delay in stopvm.

SYNOPSIS
[modified]m42/test/zaphodtestutil.py: Wait for vbox to complete poweroff.
[modified]m42/zaphod.py: Wait for vbox to complete poweroff.

DETAILS
VirtualBox's poweroff command takes some time to unlock the VM. VM operations
on the same VM will error out if performed immediately post poweroff. To
avoid this insert a delay to give time for VirtualBox to complete the task.
This is a hack. But it works for now.
[product: zaphod][project: zaphod-v0.3]: Check VM running before start/stop.

SYNOPSIS
[modified]m42/zaphod.py: Check if VM is running befor starting or stopping it.

DETAILS
The startvm operation is idempotent. If the VM is already running, the
function call has no effect. Ditto with stopvm. If the VM has already
stopped the function has no effect.