Metrics - add ctdb metrics to metrics exporter

[raghavendra-talur]

See #41 and #47

[obnoxxx]

I am not certain which metrics ctdb could expose that would be meaningful to the casual bystander/observer. Everything I am aware of that ctdb can report would only be meaningful to deep samba/ctdb experts.

For samba itself, it was a lot more obvious what to export (via smbstatus).

Loading a prometheus dashboard with metrics from ctdb could be overwhelming and unhelpful for those usually looking at it.

[phlogistonjohn]

After some time I think we'll probably come up with something. For now it's probably not worth it --- and ATM the ctdb command line tool only emits "human readable" text, where getting stats from smbstatus has been switched to use JSON.