elements-cli should suggest `-chain=X` when failing to connect to a daemon

[apoelstra]

It's super undiscoverable that you just get "connection failed" if you try connecting to the default daemon.

[apoelstra]

Maybe is an upstream bug actually..

[jsarenik]

See a filesystem-level (super fast) work-around in "bitcoin-cli here" (bch) shell script for inspiration.

This script also works wih Elemens.