Subset crashes if the get_network_patches timeouts

[samuelmanzanera]

Describe the problem you discovered

During the summary creation of the BeaconChain, if the get_network_patches timeouts, the Task.async/await crashed after 5s.
This seems due to not supervised task.

Describe the solution you'd like

We should use Task.Supervisor. async_nolink to avoid blowing up the subset's process and we should help to catch the timeout with Task.yield(task, timeout) || Task.shutdown(task)

Epic

#215