Merge PR #22692 into master

* refs/pull/22692/head:
	doc/mgr/devicehealth: document devicehealth module
	doc/rados/operations/health-checks: document DEVICE_HEALTH* messages
	mgr/devicehealth: fix style for returns
	mgr/devicehealth: use constants for health warnings
	mgr/devicehealth: deal with as many daemons as we can until limit
	mgr/devicehealth: warn if too many daemons are expected to fail soon
	mgr/devicehealth: set primary-affinity 0 for failing devices
	msg/devicehealth: fix config options
	mgr/devicehealth: only fetch osdmap once from check_health
	mgr/devicehealth: revise health messages
	mgr/devicehealth: add 'device check-health' command and run periodically
	mgr/devicehealth: fix new options
	mgr/devicehealth: add helpers to life_expectancy_response()
	mgr/devicehealth: simplify setting defaults
	common/blkdev remove debug statements

Reviewed-by: John Spray <john.spray@redhat.com>