If PhabricatorIRCBot encounters a 'nick used' error, try adding a number

Summary: Someone stole my bot's name, so the bot couldn't (re)connect. This tries adding some text to the name if it encounters a 433 'nick in use' error

Test Plan: Started a ton of bots: F154744

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9123