unit tests: added fakeroot support

Tests ending in "-runasroot" or "-runasroot.py" are run through fakeroot,
so activity that needs root privileges can be tested.

Signed-off-by: Bernardo Dal Seno <bdalseno@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>