[Reviewer: Matt][From: Alex] Refactor homestead-prov stats to cope with new homestead stats. 

Matt, please can you review this change. It covers
* Removing defunct stats and renaming the rest to start with `P_` rather than `H_`
* Moving the crest stats port to 6667
* Fixing the `LastValueCache` to publish an empty stat if it hasn't been reported yet. This behavior matches the cpp LVC implementation (and is required to stop the stats tool from timing out collecting the stat). 
* Fixing up some flake8 moans. 

Testing:
* UTs run successfully. 
* Spun up a homestead node. Used the modified stats tools to pull stats just homestead-prov, or homestead _and_ homestead-prov. Checked values looked sensible.