meson: Add 'plain' test setup
This is useful if one wants to run 'meson test' inside meta-dbus-runner.py. Doing so makes it possible to run e.g. 'meson test --gdb'.
This is useful if one wants to run 'meson test' inside meta-dbus-runner.py. Doing so makes it possible to run e.g. 'meson test --gdb'.