functional-tests: Use dbus-run-session instead of dbus-launch
From man dbus-launch
:
To start a D-Bus session within a text-mode session, do not use dbus-launch. Instead, see dbus-run-session(1).
We should use dbus-run-session instead of dbus-launch when running the functional tests.
This should allow us to simplify the test-runner.sh script.