CLI: overzealous quoting of error messages

[davidsarah]

When the CLI prints error messages from the gateway (mainly, but not always, in format_http_error), it does so using quote_output(message, quotemarks=False). This would be correct if the message were expected to be a single line, but since it is usually multi-line, the LFs are treated as control characters and escaped as \x0a. For example:

Error: 500 Internal Server Error
"Traceback (most recent call last):\x0aFailure: allmydata.mutable.common.UncoordinatedWriteError: \x0a"

instead of the intended (albeit still ugly for other reasons):

Error: 500 Internal Server Error
Traceback (most recent call last):
Failure: allmydata.mutable.common.UncoordinatedWriteError:

[davidsarah]

This bug sucks more than I thought, because it scrunches information about nested exceptions onto long unreadable lines (such as in the Description of #1670, which I edited to replace '\x0a's with newlines). It's already in the 1.10 milestone but I want to remind myself to fix it, also because it's a regression caused by being more careful about escaping generally since 1.7 or so.

[davidsarah]

Reminder to self that I really really don't want to let this one slip for 1.10.

[davidsarah]

Branch at ​https://github.com/davidsarah/tahoe-lafs/commits/1484-overzealous-quoting.

(edited to fix URL)

[davidsarah]

Fixed in ​07c26ff8 and ​ea9dfb0d.