[server] Fixed issue with private threads having the wrong name
Summary: Fixed the issue with private threads having the thread name of the userID instead of the username.
Test Plan: Tested in native and phpMyAdmin to make sure the correct thread name was set.
Reviewers: ashoat, palys-swm
Reviewed By: ashoat
Subscribers: KatPo, zrebcu411, Adrian, atul, karol-bisztyga
Differential Revision: https://phabricator.ashoat.com/D713