Root should handle its shutdown state

[afharo]

The Root class calls this.shutdown(e) when any of the lifecycle steps breaks. This allows us to gracefully shutdown Kibana when any of those steps throw an error.

The problem is that it's also called externally when a SIGTERM or SIGINT signal are emitted. So there's the possibility that we receive that signal while Kibana is still processing requests from any of its lifecycle steps.

This is causing that a signal that should make Kibana exit 0, might end up logging FATAL Error while still exiting 0 if any of the lifecycle steps throws when a condition is not met (i.e.: ES connection is closed prematurely or never properly opened yet).

IMO, we should handle the state (and potentially cancel the promises) on the first shutdown call. This can be done either in the Root class or the bootstrap.ts logic

[elasticmachine]

Pinging @elastic/kibana-operations (Team:Operations)

[elasticmachine]

Pinging @elastic/kibana-core (Team:Core)

[pgayvallet]

Fixed by #161869, closing