Add ceph plugin

The ceph plugin uses libjson-c (https://github.com/json-c/json-c) for parsing JSON from ceph daemon admin sockets. This plugin collects all output from a ceph daemon admin socket "perf dump".
No reason - this was in there before I started working on the plugin. I'll fix it (and other instances of 'strncpy') along with the type changes you suggested above.