app: Set default logger

Previously only the logger for the ovirt.* namespace was configured,
this lead to problems with plugins that reconfigured logging.
Now the logger is also configured for the root namespace.
An additional function was added to reconfigure the logging with sane
defaults.

Change-Id: I7ef89a839c9d0fc1593ff634c5f9730e68f71555
Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>