Common connection errors result in tracebacks

[dgw]

Inexperienced users simply don't have the patience and/or knowledge to dig through Sopel's output and find the cause of a connection error (e.g. #2110). They may blame Sopel for things that are outside of its control, maybe even their own fault.

It would be useful if Sopel could catch a limited set of connection problems and nudge users in the right direction. Stuff like:

• Invalid/expired SSL certificate
• Invalid address
• Hostname not found
• Connection timeout (I think this is already handled)

Of course the actual exception and traceback should still make its way to the exception log, but for purposes of user-friendliness—we claim to be a "simple" and "easy-to-use" bot, after all—terminating execution with a clear error description instead of a traceback pointing through Sopel's internals into Python stdlib code would be a good step forward.