webadmin: fix AttachStorageDomainToPool parameters

In change 881c8221 the parameters for AttachStorageDomainToPool were
changed to the new class AttachStorageDomainToPoolParameters (from
StorageDomainPoolParametersBase).
One instance of StorageDomainPoolParametersBase was left unchanged
making impossible to attach a storage domain from webadmin.

Relevant error:

ERROR [org.ovirt.engine.core.bll.CommandsFactory] An exception has
occured while trying to create a command object for command
AttachStorageDomainToPool: java.lang.Rd at:

CommandsFactory.findCommandConstructor(CommandsFactory.java:169)

Change-Id: If03b45a5fc4c5e9b64e0fa88bccb2634fb97308a
Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>