avoid KeyError when canonicaldomains is missing

[totaam]

paramiko assumes that canonicaldomains is always present when CanonicalizeHostname is set, and it errors out when it is not, preventing the whole host config from being parsed.

Xpra-org/xpra#3868 (comment)

[bskinn]

It would be good to add a test case for the bugged situation here, to guard against future regression -- is that something you could tackle, @totaam?

Also, we'll want a CHANGELOG entry for this -- please add a bullet to /sites/www/changelog.rst following the format used there.

Thanks for this!

[totaam]

I can take a look, not sure when.
(I am travelling, hence the botched conversion of the working patch into a borken PR)

[bskinn]

No worries on timeline, @totaam, happy to take care of this whenever you're able.

[totaam]

The updated PR adds a test which verifies that paramiko no longer blows up when a config specifies canonicalizehostname without also specifying canonicaldomains.

The failing check is not related to the changes I made so I am ignoring it.

[totaam]

Please review this PR, the failing test is not caused by it.

[totaam]

No worries on timeline, @totaam, happy to take care of this whenever you're able.

@bskinn how about now?