contrib/kube-prometheus: Add section on Prometheus Adapter requirements to README.md

Resolves issue #1629 in this repository.

replaced default namespaces rbac rules by a loop


set right variable name

In kubeadm 1.10 (and perhaps earlier versions, not sure), ctrl-mgr and scheduler pods' label key is `component=` rather than `k8s-app=`, which is the selector key used for kube-prometheus exporters for these components.

One of the `sed` commands for updating the kubeadm systemd
file (`/etc/systemd/system/kubelet.service.d/10-kubeadm.conf`)
was missing a `-i` reference to the file itself, causing it
to hang indefinitely if ran as declared.

I also wrapped this second `sed` in an `if grep ...` check,
in order to make the operation idempotent.

Added information on webhook token authentication and information on how to update the manifests if Kubernetes is already deployed with kubeadm.

Promnetheus -> Prometheus

* Documentation: Added kubeadm documentation #618

This getting started guide covers a simple deployment of kube-prometheus
and assumes you have deployed using kubeadm.

Hopefully this helps clears up #618

* Moved documentation to appropriate folder, updated links.

* Minor documentation editing

Fixed referneces to Alertmanager.
Slightly stronger wording on changing grafana user/pass

The AWS CLI SG commands are not necessary, kops creates an SG with these ports open to the correct SG by default

This updates prometheus to 1.7.1 where it was missing

Removed grafana restart comment from doc, as it's not necessary (grafana-watcher should pick up the changes and reload the dashboards).

Added some comments to the doc, to:
- Point the directory where make generate should be executed from
- Mention that the dashboard file should be suffixed with "-dashboard.json".
- Added hints to apply the new configMap and restart grafana

git-subtree-dir: contrib/kube-prometheus
git-subtree-mainline: 050ca21276696c8603375c699513ec487301ed62
git-subtree-split: 81c0d2f4