descriptive log for port unavailable and port-retries=0

[pallavibharadwaj]

when --port-retries=0 and the launch fails on the port, the error logERROR: the notebook server could not be started because no available port could be found. is not very appropriate. Fixes: #1914

[kevin-bates]

This change looks good - thank you.

While we're on this topic and this area of the code, I think a similar change should be made to the info message within the for loop. That is, don't issue the "trying another port" clause when retries are not desired.

[kevin-bates]

Also please edit your initial comment above to include Fixes: #1914 as the last line in the comment. This instructs git to close that Issue upon the merge of this PR. Thanks.

[pallavibharadwaj]

Edited the comment, thank you.

Is removing the trying another port part of the log a good idea, since that would be consistent with Permission to listen on port 403 denied? Or would you suggest having this clause in both the cases?

[kevin-bates]

I'm only suggesting the clause's removal when self.port_retries == 0. When non-zero we should indicate other ports will be attempted, but not when retries are disabled. I believe the permission message is fine as-is - although I suppose one could argue that it too should include the 'trying another port` clause (only when retries are enabled). That said, you typically want to provide only the necessary information in security-related messaging, so perhaps leaving that one alone is probably best given it didn't include the clause in the first place.

[pallavibharadwaj]

@kevin-bates - I have added the changes you suggested, in the PR. I made a new commit instead of rebasing, in order to highlight my new changes. I will rebase the commits if needed after you approve it. Thank you.

[kevin-bates]

LGTM - thank you for you first contribution! 🎉

[Zsailer]

LGTM!