APIcast strips request path for proxied https requests

Issue

• APIcast strips the path from requests when the following conditions are met:
  • APIcast is configured with an https proxy for Upstream traffic
  • The Backend is configured with the Public Path: /
  • The Upstream is configured with https:// scheme and a path in its Private URL, as the following example: https://echo-api.3scale.net/some/path
• Considered the configuration above, a request to https://<PUBLIC_BASE_URL>/foo/bar would be routed to https://echo-api.3scale.net/some/path instead of https://echo-api.3scale.net/some/path/foo/bar