CMakeLists: use existing install path variable; honour BUILD_TESTING

Authored by dfaure on Aug 14 2018, 1:35 PM.

Description

CMakeLists: use existing install path variable; honour BUILD_TESTING

Summary:
for consistency with KF5 frameworks

This file could be much further simplified if the Qt4 support can be removed...

Test Plan: builds

Reviewers: vkrause

Reviewed By: vkrause

Differential Revision: https://phabricator.kde.org/D14833

Details