mgr: report health check changes immediately

mgr: report health check changes immediately

Currently beacons and reports are sent periodically, which means that
health check changes made by modules are only visible to the monitor
after a delay. This patch sends a health report immediately after a
change occurs.

1. decouple scheduling of reports from beacons
2. moves report scheduling into DaemonServer
3. exposes a "send now" option
4. health check change detection triggers immediate report

Signed-off-by: Noah Watkins <nwatkins@redhat.com>