vz: implementation of attach/detach network devices
    
    In this patch we add VIR_DOMAIN_DEVICE_NET handlers implementation
    for domainAttachDevice and domainDetachDevice callbacks.
    
    As soon as we don't support this operation for hypervisor type domains,
    we implement this functionality for containers only.
    
    In detach procedure we find network device by MAC address.
    Because PrlVmDevNet_GetMacAddress() returns MAC as a UTF-8 encoded
    null-terminated string, we use memcmp() to compare it.
    Also we remove corresponding virtual network by prlsdkDelNetAdapter call.