Arcyd: fill out 'no_users_on_branch' string

Supply a more useful comment when reporting that no email addresses were
recognised on a branch.

Test Plan: $ ./precommit.sh
phldef_conduit: use 600 second timeout on urlopen

Arcyd has been observed to hang for hours when communicating with
Conduit.  Introduce a timeout to limit the amount of time we can be
stuck on a blocking communication.

Test Plan: $ ./precommit.sh