Fixes a bug where an allocation is considered healthy if some of the
tasks are being restarted and as such, their checks aren't tracked by
consul agent client.
Here, we fix the immediate case by ensuring that an alloc is healthy
only if tasks are running and the registered checks at the time are
healthy.
Previously, health tracker tracked task "health" independently from
checks and leads to problems when a task restarts. Consider the
following series of events:
1. all tasks start running -> `tracker.tasksHealthy` is true
2. one task has unhealthy checks and get restarted
3. remaining checks are healthy -> `tracker.checksHealthy` is true
4. propagate health status now that `tracker.tasksHealthy` and
`tracker.checksHealthy`.
This change ensures that we accurately use the latest status of tasks
and checks regardless of their status changes.
Also, ensures that we only consider check health after tasks are
considered healthy, otherwise we risk trusting incomplete checks.
This approach accomodates task dependencies well. Service jobs can have
prestart short-lived tasks that will terminate before main process runs.
These dead tasks that complete successfully will not negate health
status.
* client: improve group service stanza interpolation and check_restart support
Interpolation can now be done on group service stanzas. Note that some task runtime specific information
that was previously available when the service was registered poststart of a task is no longer available.
The check_restart stanza for checks defined on group services will now properly restart the allocation upon
check failures if configured.
Some of the context uses in TR hooks are useless (Killed during Stop
never seems meaningful).
None of the hooks are interruptable for graceful shutdown which is
unfortunate and probably needs fixing.
