Support 'InvalidPowerState' exception
Support 'InvalidPowerState' exception

The aforementioned exception is used to determine if a VM is
already powered on. This was introduced in the spwan refactor:
https://review.openstack.org/#/c/83207/.

Change-Id: I35fa88cdae5d488d0dbf65346aa5903e5eec17fb

openstack/oslo.vmware