don't load identity in offline mode (temp)

**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.
core context + cancels

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