Zk kafka plugins

Add a zookeeper config plugin to load json string config from zookeeper;

Add a kafka log receiver plugin, the plugin can only send messages less then 900 Bytes each time. The plugin is not actually practical at the moment, may someone help to figure out a proper way to code with LibKafka.

Yours,
Imcom
Not sure what this is for yet, but I don't like defining `osquery::config` as a string here. Might collide with something innocently one day.