JCLOUDS-223: Implement token based auth in Abiquo

Properly implemented token based authentication. An initial request
is performed using Basic Authentication to request an authentication token.
Subsequent requests will use the obtained token to authenticate, and once
it expires a new one will be automatically requested.
Removed unused search service in Abiquo
Added missing throw to Throwables.propagate
JCLOUDS-205: Do not create duplicated groups in Abiquo

Refactored the AbiquoComputeServiceAdapter to avoid creating
more than one group with the same name, when creating multiple
nodes concurrently.