Remove node interface down

This alert is not specific enough on the interfaces it selects which in
turn makes it too noisy.

Add missing adapter to build snippet

Remove grafana-image

It's long obsolete

These metrics can still be valuable to troubleshoot components running
in cgroups on the host, outside the scope of Kubernetes pods.

Fix go get jsonnet command.

cAdvisor exposes metrics for each cgroup hierachy step, and containers
are part of the respective pod's hierarchy, causing double accounting
when not filtered appropriately.

Fix node:node_disk_saturation rules to return value in seconds

Update travis to latest minikube, k8s, jsonnet

Adding kustomization files for remote bases

Follow other snippet file extension names
This file is not referenced from other location in repo according to
quick grep.

* [Modified] Makefile to run kustomize.jsonnet
* [Modified] Moved kustomization from example.jsonnet to
examples/kustomize.jsonnet
* [Modified] kustomization file to land at root of kube-prometheus so
current users can continue to use `kubectl apply -f manifests`

Closes #2391

Adds support to allow kustomize users to point to a [remote
base](https://github.com/kubernetes-sigs/kustomize/blob/master/examples/remoteBuild.md) of the prometheus-operator and kube-prometheus. Now that kustomize is a part of kubectl, this is provides a very simple way of installing prometheus-operator and kube-prometheus with no additional tools besides kubectl.

* [Added] kustomization.yaml: hardcoded kustomization base for prometheus-operator
bundle.yaml
* [Added] kustomization generation from kube-prometheus example jsonnet

contrib/kube-prometheus: Update Prometheus, Thanos & Grafana

Use recommended addon-resizer 1.8.4