Fixing requests for HTTPS sites in http_requests.py

Hello OONIProbe devs,

If I specify an HTTPS URL as an argument in http_requests.py, it looks like some of the input processing in httpt.py turns the URL scheme into "shttps", which causes problems in ooni/utils/txagentwithsocks.py and raises a SchemeNotSupported exception.  I've tweked it and tested it, and it seems to work fine on my fork.  Let me know if you want any changes made.