TS-1770 Guess scheme if blank when looking up remap rules

When connecting to https sites using ATS as a forward proxy, the CONNECT
method is used, and the URL doesn't have a scheme (http/https) present. When
using remap.config to limit which sites ATS will proxy for, there is no rule
that can be made to match an a request without a scheme present, and so no way
to allow requests to a https site.

This commit lets ATS assume a scheme (https by default, http if on port 80)
if one isn't given for the purposes of looking up remap rules.