Improve monitoring e2e test.
Up cmd/e2e timeout

Attempt to fix https://github.com/GoogleCloudPlatform/kubernetes/issues/3053
Fix binary detection on GKE

* kubectl is kubectl.sh in the e2es, so not needed in the path
* Use the environment variable, and try to make sure the preview
component is installed.
Rename namespaceAsPath
Merge pull request #3082 from zmerlynn/gkecmd

Fix binary detection on GKE
Merge pull request #3081 from zmerlynn/i3053

Up cmd/e2e timeout
Merge pull request #3079 from vishh/fix_monitoring

Improve monitoring e2e test.
Merge pull request #3093 from derekwaynecarr/more_client_updates

Follow-up review comments from 3066
Adjust the PATH to the right kubectl for gcloud, add KUBECTL_PATH override

Force kubectl to the git repo version if we detect a built version.
Add a KUBECTL_PATH override so that system/home directory versions of
kubectl can be used if desired. Remove existing $HOME inference.
Merge pull request #3092 from zmerlynn/gke-kubectl-path

GKE: Adjust the PATH to the right kubectl for gcloud