vz: implementation of attach/detach network devices

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.