Show hostname in krfb connection info

Summary:
Using krfb as desktop support tool for ~250 desktops on LAN - 95% of the users aren't equipped to deal with reciting IP addresses accurately, so I wanted to add the hostname into the connection details as well, since it's easier for non-tech people to read that back.

Attached patch does this, and works internally for us - thoughts on doing it better:
* hostnames as reported by the host are not necessarily accurate for network access, so
* consider actually doing a nameserver lookup to verify
* only show the hostname if you can verify

Reviewers: ngraham, #kde_applications, aacid

Reviewed By: #kde_applications, aacid

Subscribers: akulichalexandr, aacid, pino, alexeymin

Tags: #kde_applications

Differential Revision: https://phabricator.kde.org/D14527