JCLOUDS-171: Fixed NPE when destroying nodes in Abiquo

There was a race condition when destroying a node in Abiquo
using the ComputeService: jclouds performed the active wait
until the node was in state TERMINATED, and used the transformation
functions to convert an Abiquo VirtualMachine to a NodeMetadata. If the
node was effectively deleted during this transformation, a NPE
was raised. This is because there are a couple of API calls that are
executed in that transformation to retrieve all information required
to build the NodeMetadata.

To prevent this, the AbiquoComputeServiceAdapter will block until the
node has been actually deleted instead of delegating that to jclouds.
This way there is no need to run the transformation functions that had
the race condition.