Correctly handle override claims.

We were not blowing away override claims when we should have been.
HostManager to track hosts and when they go offline.

Tracks pings by hosts and detects offline hosts as those that have
not checked in within the last 15 seconds.
Correctly handle hosts going offline

Uses the HostManager to track pings from hosts requesting queue
lists and to invalidate the matrix queue allocation whenever a
host has not checked in for some time (default 15 seconds).

This will allow for correct elastic configuration as workers go
 up/down
Merge pull request #12 from PeopleAdmin/host_checkin_freshness

Host checkin freshness