Fleet agent failed to connect to fleet server after assigning new agent policy

[pingz (Ping Zhang)]

Hi there:

I have fleet agent and fleet server (7.15.0) both running as pods in Kubernetes.  After applying new agent policy, fleet agent became offline.  I can see the error in fleet agent log

|2021-10-08T15:56:56.120Z|INFO|stateresolver/stateresolver.go:66|Updating internal state|
|---|---|---|---|
|2021-10-08T15:56:56.217Z|ERROR|fleet/fleet_gateway.go:180|failed to dispatch actions, error: acknowledge 1 actions '[action_id: policy:b6167280-284d-11ec-af8e-31c20ea2b163:3:1, type: POLICY_CHANGE]' for elastic-agent '4df9cba7-a5a5-4751-b244-329600b37e3b' failed: fail to read original error: read tcp 10.250.73.70:58468->172.20.153.42:8220: read: connection reset by peer|
|2021-10-08T15:56:56.217Z|ERROR|status/reporter.go:236|Elastic Agent status changed to: 'error'|
|2021-10-08T15:56:57.724Z|ERROR|fleet/fleet_gateway.go:205|Could not communicate with fleet-server Checking API will retry, error: fail to read original error: read tcp 10.250.73.70:58554->172.20.153.42:8220: read: connection reset by peer|
|2021-10-08T15:56:58.723Z|INFO|log/reporter.go:40|2021-10-08T15:56:58Z - message: Application: metricbeat--7.15.0--36643631373035623733363936343635[4df9cba7-a5a5-4751-b244-329600b37e3b]: State changed to RUNNING: Running - type: 'STATE' - sub_type: 'RUNNING'|
|2021-10-08T15:57:13.327Z|INFO|stateresolver/stateresolver.go:48|New State ID is cgfC5hHh|
|2021-10-08T15:57:13.327Z|INFO|stateresolver/stateresolver.go:49|Converging state requires execution of 3 step(s)|