Remove unused stats, rename existing ones (to not clash with new homestead) and tidy up flake8 moans
Improve commenting
Merge remote-tracking branch 'origin/master' into stats_refactor
Merge remote-tracking branch 'origin/master' into stats_refactor
Publish an empty statistic if no cached value found
Merge pull request #153 from Metaswitch/stats_refactor

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