D18222: Don't hardcode dbus policy install dir

[Aleix Pol Gonzalez]

apol accepted this revision.
This revision is now accepted and ready to land.

REPOSITORY
  R283 KAuth

REVISION DETAIL
  https://phabricator.kde.org/D18222

To: arojas, #frameworks, apol
Cc: kde-frameworks-devel, michaelh, ngraham, bruns