[runit] make runsv tests in runit suite more accurate
[runit] remove pid dumping bits

a) it's clear that service restarts are being triggered reliably
b) it's clear that the related test can give false positives since
   we dont cleanup after outselves
[runit] rework sensu_service provider to support standard enable, start, stop and restart actions
[runit] modify service recipes to use action [:enable, :start]