1. Unhide ConnectivityManager.getDefaultProxy() and update it to
take into account process-bound-Networks.
2. Deprecate EXTRA_PROXY_INFO and instead encourage querying via
getDefaultProxy().
Bug: 17905627
Bug: 17420465
Bug: 18144582
Change-Id: I45358ee82fe705d048022c8238b2452f52c37b88