Instead of just reporting that a task failed get the
localized message from the TaskInfo error and include
it in the reported error message.

Implement minimal deserialization support for the
MethodFault type in order to obtain the actual fault
type.

For example, this changes the reported error message
when trying to create a volume with zero size from

  Could not create volume

to

  Could not create volume: InvalidArgument - A specified parameter was not correct.

Not perfect yet, but better than before.