K8S: better error handling for evicted pods

[oavdeev]

From testing on our EKS cluster, it turns out container_statuses can sometimes be None for a failed pod. It looks like it happens when the pod was assigned to a node, haven't had a chance to start the containers yet, and gets evicted. In that case current version fails with a non-descriptive error ("NoneType not subsciptable" and a stack trace). This PR adds a handler for this case and prints a nicer error message, derived from V1PodStatus.reason:

...
2021-09-21 20:27:10.659 [6617/start/117133 (pid 14120)] Kubernetes error:
2021-09-21 20:27:10.660 [6617/start/117133 (pid 14120)] Evicted: Pod The node had condition: [DiskPressure]. . This could be a transient error. Use @retry to retry.
2021-09-21 20:27:10.760 [6617/start/117133 (pid 14120)]

This condition is somewhat tricky to repro without running the full test suite, so for reference, here's how V1PodStatus looks like in those cases, as returned by K8S API:

    ...
    "status": {
        "conditions": None,
        "container_statuses": None,
        "ephemeral_container_statuses": None,
        "host_ip": None,
        "init_container_statuses": None,
        "message": "Pod The node had condition: [DiskPressure]. ",
        "nominated_node_name": None,
        "phase": "Failed",
        "pod_ip": None,
        "pod_i_ps": None,
        "qos_class": None,
        "reason": "Evicted",
        "start_time": datetime.datetime(2021, 9, 17, 2, 26, 4, tzinfo=tzlocal()),
    },