serve command (http api)

Caused panic.

Feat/snappy cmd

(test was failing)

Erroring out in core setup should cancel the context
to ensure subsystems are shut down. This has to happen
all over the place we use contexts.

@perfmode @whyrusleeping

**For now**, we don't need to load/parse the private key
(which causes a signficant delay in commands) when doing
things entirely offline. This may change, and in that case
the private key should be loaded on demand.