[http kio slave] use QSslSocket instead of KTcpSocket (deprecated)
Summary: Depends on D24928
Test Plan: make && ctest
Reviewers: dfaure, vkrause
Reviewed By: vkrause
Subscribers: kde-frameworks-devel
Tags: Frameworks
Maniphest Tasks: T11544
Differential Revision: https://phabricator.kde.org/D24873