At the moment there is a hack in the implementation of GetMachineId()
to stop tests from failing during "make check" on a system where
dbus has never been installed, by silently generating a new unique
fake "machine ID" for each process. I'm about to change that
behaviour to report errors properly; skip affected test-cases if we
can't read the real machine ID.

The shell scripts to test dbus-launch are run both as "make check"
tests (for which it is valid for dbus to be not correctly installed)
and as installed-tests (for which that is not valid), so make them
pass during "make check" but fail during installed testing.
The tests in bus/ and test/name-test/ are only run during "make check"
so they only have the code path where they are skipped.

Signed-off-by: Simon McVittie <smcv@collabora.com>
Reviewed-by: Philip Withnall <withnall@endlessm.com>
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=13194