Handle epoll errors when handling device events

[iulianbarbu]

At the moment, the current device event handling implementation, for net, block and vsock devices, does not handle errors which might occur on the epoll registered event fds (EPOLLHUP, EPOLLRDHUP, EPOLERR). We must unregister these fds for which we receieved error events.

[acatangiu]

I don't think we should unregister in case of any of those events. But all devices do need to gracefully handle them.

L.E. apparently the EPOLLHUP cannot be consumed and the fd must be unregistered from epoll otherwise it will keep pinging.

[serban300]

In the meanwhile we switched to using the EventHandler from rust-vmm. We should check if it handles these events or if we should move this issue there.

[JonathanWoollett-Light]

As @serban300 mentioned we now use https://github.com/rust-vmm/event-manager. Closing as this issue does not relate to Firecracker code.