Tests: event-notifier: multi UID error accounting support

The new test case adds one root trigger and one regular user trigger as
well as apps from both of these users.

The test then confirm that the error accounting of the root trigger
reports what is happening on the regular user's app as well as its own
app.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: Iaec231863de98b14891602bdae010449989de6f9