Improve error message when VMs are absent

[kzys]

Right now, it may only return ttrpc: closed: unknown. We probably should return something more meaningful/helpful.

[richiewahidin]

Hi I am a student in UT Austin and I am interested in working on this issue for my Virtualization project. Can you assign this issue to me?

[BinSquare]

We should unlock this filter within ttrpc to emit more specific?: https://github.com/containerd/ttrpc/blob/944ef4a40df3446714a823207972b7d9858ffac5/client.go#L399

As it stands, it basically returns "ErrClosed" or ttrpc: closed for all cases except if error is nil.

To add on, this current msg tells us the connection is closed but we don't have any additional information on why it's closed.

A piece of information that ends up getting wrapped specifically would be helpful is if it's ECONNRESET, seems like we should try to reconnect in that case?