make rt-mailgate use https instead of http to talk to RT

this makes things work on new RT with the existing Apache
redirects to https (it doesn't like http 301 there)

and it also works on existing old RT on streber without other changes.

root@streber:
/usr/bin/rt-mailgate: connecting to
https://rt.wikimedia.org/REST/1.0/NoAuth/mail-gateway

Change-Id: I7d11c2bc1367a34b516588d6d0e7f192a87ccdb5
okTicket: 5167Queue: ops-requests