Add src/linux/integration-test: This is a Python unittest based test suite
which provides methods for building a sandbox sysfs tree, runs upowerd
in it, and checks for correct properties.
As it is really hard to provide fake uevents, this currently only works for
properties which do not depend on dynamic system changes, i. e. you can
currently only check the status after coldplugging.
However, this already provides enough possibilities for functionality and
regression testing, and exposes some bugs with determining the "OnBattery"
property under certain conditions like the ones described in
<https://bugs.freedesktop.org/show_bug.cgi?id=24371>.
If any of the tests fails, the daemon log will be printed to stderr for easier
debugging.
With the previous commit that adds "upowerd --test", we can also run
the integration tests as non-root. If they are called as root, start upowerd
normally on the system bus, otherwise on the session bus with --test.
e1f4aa38de