Multicast group verification

Verification will be done for multicast group provided as cluster attributes.
As for now it will be done as part of network verifcations workflow on Fuel UI.

Multicast verification will be performed only for network which is used by corosync for communication - management in fuel terms.

In general workflow will be next:
1. Start networks verifications from fuel-client or fuel ui.
2. Prepare configuration from cluster.attributes corosync and network interfaces used by management network by each node.
3. Send prepared config for each node to orchestrator.
4. Orchestrator sends multicast_listen actions to each agent.
5. Agent connects to specific multicast group, and starts packets sniffer.
6. Orchestrator sends multicast_send to each agent - agent sends packets to multicast group.
7. Orchestrator sends multicast_info to each agent - agent sends back to orchestrator lists of responses from each node.
8. Received responses sended back to nailgun, where decesion about multicast connectivity is made, if it was succesfull cluster.attributes.corosync.verified will be set to True.