This means that logging will be completely disabled until log_init()
has been called, which is useful to prevent log spam when running
UNITTEST{} blocks in debug builds.
Note that this doesn't change the default log level at runtime, which
was already being set to LOG_CLASS_INFO in main.c and client.c.
The new log level is also exposed to the command-line interface as
`--log-level=none`, which allows disabling logging entirely.
