Mark cluster status failed when no pods are running or quorum is lost

[Marlinc]

Clusters that currently have all their pods killed or have lost
quorum will stay in a running phase while being completed dead.

This change marks the corresponding errors as being fatal which
lets the operator mark those clusters as failed.

Fixes coreos#2067, coreos#1973

Example status:

Status:
  Client Port:  2379
  Conditions:
    Last Transition Time:  2019-11-11T20:03:43Z
    Last Update Time:      2019-11-11T20:03:43Z
    Reason:                Cluster available
    Status:                True
    Type:                  Available
  Current Version:         3.2.25
  Members:
    Ready:
      etcd-cluster-64687hxm2r
      etcd-cluster-klb4cjqbbb
      etcd-cluster-qcfpqm495v
  Phase:           Failed
  Reason:          all etcd pods are dead.
  Service Name:    etcd-cluster-client
  Size:            3
  Target Version:  

Please read https://github.com/coreos/etcd-operator/blob/master/CONTRIBUTING.md#contribution-flow