Nothing measured the host itself. hive-c0re emits per-container metrics
and each service exports its own, so the store could answer 'is this
container using more memory than last week' and could not answer 'is the
machine under them out of memory' -- the question every one of those
readings is implicitly relative to.
Hive tier rather than swarm: a host is owned by the hive running on it,
and the swarm tier runs one collector for the whole swarm, so it would
have to reach other machines to see theirs.
Every scraper the pinned receiver offers except process, which adds a
series set per running process -- unbounded on a hive host, where the
nine shipped are a fixed handful. Coverage and cardinality are different
axes and only the second can hurt the store.
Refs #3649
d9f09f4a52