Report aeflex services discovered before errors

[stephen-soltesz]

The current logic in the aeflex service discovery collects services incrementally. Unfortunately, if any one encounters an error, all services discovered up to that point are ignored and only the error is returned.

This behavior was observed in production, when metrics from the locate AEFlex service were not discovered b/c of an error scanning the "locate-platform" service.

Ideally, the discovery process could log errors, and report any previously discovered services.

2022/07/27 16:29:04 apps/mlab-sandbox/services/default versions: 6 active: 0 inactive: 0
2022/07/27 16:29:05 apps/mlab-sandbox/services/locate versions: 2 active: 2 inactive: 0
2022/07/27 16:29:05 apps/mlab-sandbox/services/locate-platform versions: 79 active: 0 inactive: 0
2022/07/27 16:29:05 Error: *aeflex.Service: googleapi: Error 400: The requested Compute resource is not found.
Details:
[
  {
    "@type": "type.googleapis.com/google.rpc.PreconditionFailure",
    "violations": [
      {
        "description": "Request to https://compute.googleapis.com/compute/v1/projects/projects/mlab-sandbox/regions/us-east1/instanceGroupManagers/aef-locate--platform-20220420t140553-00/listManagedInstances?key\u0026maxResults=50 failed, details: The resource 'projects/mlab-sandbox/regions/us-east1/instanceGroupManagers/aef-locate--platform-20220420t140553-00' was not found",
        "subject": "COMPUTE",
        "type": "RESOURCE_NOT_FOUND"
      }
    ]
  }
]
, failedPrecondition