forceRenameUsers: Replace _ in database name with -
Underscores (_) are not valid in usernames, and are normally replaced
with spaces. But those look funny to some people, so use dashes (-)
instead. Also canonicalize the username so we don't end up with invalid
usernames in the database.
(cherry picked from commit f34230a3dbebe849a3cd98b15a3135ada3848fae)