gke auth config-helper is hitting against too many open files

@andyshinn reported following error during `kapp deploy`.

```
Error: Listing schema.GroupVersionResource{Group:"certificates.k8s.io", Version:"v1beta1", Resource:"certificatesigningrequests"}, namespaced: false: Get https://x.x.x.x/apis/certificates.k8s.io/v1beta1/certificatesigningrequests?labelSelector=kapp.k14s.io%2Fapp%3D1565298894854176000: error executing access token command "/usr/local/Caskroom/google-cloud-sdk/latest/google-cloud-sdk/bin/gcloud config config-helper --format=json": err=pipe: too many open files output= stderr=
```

it appears that number of allowed open fds is exceeded due to gke auth.

Start by reproducing the failure during `kapp deploy` with GKE authentication and inspect file-descriptor usage around `gcloud config config-helper --format=json`. Trace how the authentication command is invoked and confirm that repeated Kubernetes API access does not exhaust open files; done when the reported error no longer occurs under the same conditions.

Written by the indexing model from the issue text.