[4.15] CEO aliveness check should only detect deadlocks

From a test run in [1] we can't be sure whether the call to etcd was really deadlocked or just waiting for a result.

Currently the CheckingSyncWrapper only defines "alive" as a sync func that has not returned an error. This can be wrong in scenarios where a member is down and perpetually not reachable. 
Instead, we wanted to detect deadlock situations where the sync loop is just stuck for a prolonged period of time.

[1] https://gcsweb-ci.apps.ci.l2s4.p1.openshiftapps.com/gcs/test-platform-results/logs/periodic-ci-openshift-release-master-nightly-4.16-upgrade-from-stable-4.15-e2e-metal-ipi-upgrade-ovn-ipv6/1762965898773139456/

>4.14

Always

    1. create a healthy cluster
    2. make sure one etcd member never responds, but the node is still there (ie kubelet shutdown, blocking the etcd ports on a firewall)
    3. wait for the CEO to restart pod on failing health probe and dump its stack
    

CEO controllers are returning errors, but might not deadlock, which currently results in a restart

CEO should mark the member as unhealthy and continue its service without getting deadlocked and should not restart its pod by failing the health probe