http: Populate HTTPS environment variable.

So "wsgi.url_scheme" gets the correct value.

caucase/http.py

@@ -79,6 +79,7 @@ class CaucaseSSLWSGIRequestHandler(CaucaseWSGIRequestHandler):
   ssl_client_cert_serial = '-'
   def get_environ(self):
     environ = CaucaseWSGIRequestHandler.get_environ(self)
+    environ['HTTPS'] = 'on'
     client_cert_der = self.request.getpeercert(binary_form=True)
     if client_cert_der is not None:
       cert = x509.load_der_x509_certificate(