search lib paths for boltd for debian systems

Summary:
on ubuntu 0.5 the path may be usr/lib/$archtriplet/boltd or
usr/lib/bolt/boltd depending on the specific series.
on debian it's always usr/lib/bolt/boltd right now.

Test Plan: correctly found boltd on ubuntu 18.04

Reviewers: dvratil

Reviewed By: dvratil

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D21873