Added generic refresh method in Abiquo

In Abiquo every object contains a link to itself with rel="edit". This
commit adds a generic method in the DomainWrapper base class that reads
the link and performs a GET operation to refresh the object.

This method was already used in conversions and virtual machines, and
now every object will have it implemented.
Updated Rackspace Cloud Load Balancers doc.
Merge pull request #1310 from nacx/refresh-objects

Added generic refresh method in Abiquo
Merge pull request #1311 from abiquo/VirtualMachineTemplateTest

Set the cost code field to avoid accidental test failures
Merge pull request #1313 from rackspace/rax-clb-docs

Updated Rackspace Cloud Load Balancers doc.
Expose resource creation date
Merge pull request #1314 from maginatics/creation-date

Expose resource creation date
VM.nameLabel property is mandatory in Abiquo