virsh-domain: update attach-interface to support type=hostdev
    
    Adding this feature will allow users to easily attach a hostdev network
    interface using PCI passthrough.
    
    The interface can be attached using --type=hostdev and PCI address or
    as --source.  This command also allows you to tell, whether the interface
    should be managed.
    
    Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=997561
    
    Signed-off-by: Pavel Hrdina <phrdina@redhat.com>