JCLOUDS-156: Cleanup Abiquo provider

Removed legacy and trivial code from the Abiquo provider:

* Removed all trivial predicate classes.
* Removed all find* and list* methods in the domain objects that did
  nothing but delegating to Guava Iterables.
* Removed UCS and Pricing Apis, since they are out of the scope of the
  provider.
* Moved monitor events to the existing monitor package.
JCLOUDS-146: Refactored asynchronous tasks in Abiquo

Refactored asynchronous tasks to be generic, and created a
concrete task class for each existing task type.
This way, all operations will produce a typed task, and operating
with it will be easier. This will also allow to get the results
produced by the task.