Refactor GCE wrapper library to allow execution from E2E test suite

This reverts commit 147b6911f5, reversing
changes made to 6fd986065b.

hack/ginkgo-e2e.sh

@@ -97,6 +97,7 @@ export PATH=$(dirname "${e2e_test}"):"${PATH}"
   --provider="${KUBERNETES_PROVIDER}" \
   --gce-project="${PROJECT:-}" \
   --gce-zone="${ZONE:-}" \
+  --gce-service-account="${GCE_SERVICE_ACCOUNT:-}" \
   --gke-cluster="${CLUSTER_NAME:-}" \
   --kube-master="${KUBE_MASTER:-}" \
   --cluster-tag="${CLUSTER_ID:-}" \

hack/verify-flags/known-flags.txt

@@ -105,6 +105,7 @@ func-dest
 fuzz-iters
 gather-resource-usage
 gce-project
+gce-service-account
 gce-zone
 gke-cluster
 go-header-file