RPC errors should not be ugly on the iroh CLI

[faassen]

Ugly is defined as:

• A nice enough looking Error: foo where the text foo is incomprehensible/plain wrong

• An ugly looking programmer-style output.

• A crash

The List

• iroh get CID/does/not/exist results in a weird error message
• connection issues Iroh CLI better error for connection refused #145

Connection problems ugly output:

Error: status: Unavailable, message: "error trying to connect: tcp connect error: Connection refused (os error 111)", details: [], metadata: MetadataMap { headers: {} }

Caused by:
    0: transport error
    1: error trying to connect: tcp connect error: Connection refused (os error 111)
    2: tcp connect error: Connection refused (os error 111)
    3: Connection refused (os error 111)

[b5]

part of the issue surrounds RPC error handling, which is nontrivial. Errors should be better with the switch to tarpc (see #95).

Let's repurpose this issue to be specifically about errors stemming from RPC connections, and making them not gross