trackertestutils: Add an optional D-Bus system bus to the sandbox

This allows us to work with umockdev to simulate hardware events.
3 jobs for sam/umockdev in 2 minutes and 23 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Test
passed #733031
test-alpine-edge

00:01:16

passed #733032
test-fedora-latest

00:02:22

passed #733033
test-ubuntu-rolling

00:01:09