Log level can be set on specific module (routing, dhcp, loadbalancing..)
or for all supported modules.
Setting log level to 'none' will disable logging.
Setting log level to debug/info/warning/error will enable logging with
corresponding level.
Change-Id: Ic4271bd60ace0b319d92bf6c92b3a8e42bcebcb7
59f2258c1a