Make ATC lists sort E-mails with preferred first

* tools/atc/email-stats.py: Adjust the order in which Gerrit E-mail
addresses are returned so that the one listed as the preferred
address is sorted to the beginning of the set.

Change-Id: I95b5817ada58f4059df4f5c0b406183f1c1e5b74
Merge "Make ATC lists sort E-mails with preferred first"