Since the foundation sometimes needs to deduplicate subsequent
invitations for the same foundation member against invitations sent
by another system, use the member ID as the first field of the
invite instead of using the Gerrit username now that we have that
information available. Use a default member ID of 0 to indicate
non-member invitees who may require additional manual deduplication
or vetting. Also log the member ID in the output of the invite mass
mailer script.
Change-Id: I86d879a5f06144a0889eb852f2cf3d555a12a7aa