Add an option for port re-using

[VladimirKuzmin]

❓ I'm submitting a ...

• [ ] 🐞 bug report
• [X] 🐣 feature request
• [ ] ❓ question about the decisions made in the repository

🐞 Is your feature request related to a problem? Please describe. We have a process that automatically distributes available ports across multiple cheroot processes and keeps sockets on those ports opened until cheroot processes take control on them. Cheroot right now cannot reuse those opened ports.

🐣 Describe the solution you'd like Add an option to say cheroot to set SO_REUSEPORT socket option.

📋 Describe alternatives you've considered Passing socket object to cheroot instead of bind address, but that would require some refactoring and I don't think it would follow Zen of Cherrypy if this solution would be ported to cherrypy.