Rather than calling virDomainHostdevAssignAddress during the parsing
of the XML, move the setting of a default hostdev address to domain/
device post processing.

Since the parse code no longer generates an address, we can remove
the virDomainDefMaybeAddHostdevSCSIcontroller since the call to
virDomainHostdevAssignAddress will attempt to add the controllers
that were not already defined in the XML.

This patch will also enforce that the address type is type 'drive'
when a SCSI subsystem <hostdev> element is provided with an <address>.
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>