cli: print nicer message when miner hasn't initialized

[jsign]

Fixes #810
The GH issue has a little history of this error that has popped in Slack channel a few times.

Feels like this peer.ID("SETME") should be a constant somewhere. The other place that is used is in lotus-fountain. If there's a clear place to put it, I can change it.

[magik6k]

Good catch, I'm not sure if we want to hardcode that string as 'not initialized', even though it should be fine.

@Kubuxu @whyrusleeping opinions?

[whyrusleeping]

eh, no strong opinions, though maybe we do a length check and say "if the peer ID isnt above the minimum real peerID length, its not initialized" or something?

[jsign]

eh, no strong opinions, though maybe we do a length check and say "if the peer ID isnt above the minimum real peerID length, its not initialized" or something?

I guess that if the only time a peer.ID can have an invalid value is SETME, it would be better to keep checking for that particular value to output this message.

Maybe doing the length check won't make apparent future invalid values introduced by some buggy behavior... better to get the weird output again than confuse it with this scenario.