prometheus: Enable live migration of rule configmaps to rule file crds

With this patch the Prometheus Operator checks if there are any
Kubernetes ConfigMaps inside the Prometheus namespace which fullfill the
`Spec.RuleSelector` requirement. If so, it creates a RuleFile for each
key in the `ConfigMap.Spec.Data` map inside the Prometheus namespace.

Adds proxy_url to v1.Endpoint. Fixes #1385

Migrate alerts

Make certgen work on OSX

These alerts will be vendored in the future through jsonnet-bundler
directly from the etcd repository.

Cleanup

fix doc guide link of kube-prometheus

kube-prometheus: add the watch verb (to the namespace apiGroup for the prometheus-operator ClusterRole).

Also checking in the changes made to prometheus-rules.yaml by "make generate", in order to (hopefully) get the build to be green.

After modifying prometheus-operator.libsonnet (see commit ec19c16), these are the changes that were made to 0prometheus-operator-clusterRole.yaml by running "make generate".

To get the "Failed to watch" error to stop happening in the prometheus-operator logs.

Fixes #1324 for kube-prometheus.

prometheus: Introduce RuleFile Custom Resource Definition 

This patch introduces a new Custom Resource Definition to the
Prometheus Operator - the Rule CRD. It addresses two main
needs:

1. Prometheus (alerting and recording) Rule validation during creation time
via Kubernetes Custom Resource Definition validation.

2. Life-cycle management of Prometheus application Rules alongside the
application itself, inside the applications Kubernetes namespace, not
necessarily the namespace of the scraping Prometheus instance.

A user defines Prometheus alerting and recording Rules via a Kubernetes
Custom Resource Definition. These Custom Resource Definitions can be
fully validated by the Kubernetes API server during creation time via
automatically generated OpenAPI specifications. Instead of the
restriction of a Prometheus instance to only select Rule definitions
inside its own namespace, the Prometheus specification is extended to
also specify namespaces to look for Rule Custom Resource Definitions
outside its own namespace.

---

Dependent technical changes:

- prometheus: Use github.com/jimmidyson/configmap-reload to reload rules

- prometheus: Remove Prometheus Statefulset deletion function. Starting
with K8s >=1.8 this is handled via OwnerReferences.

- prometheus: Do not add rule files checksum to Prometheus configuration
secret

- prometheus: Update StatefulSet only on relevant changes. Instead of
updating the Prometheus StatefulSet on every `sync()` run, only update
it if the input parameters to `makeStatefulSet` change.  Enforce this
via a checksum of the parameters which is saved inside the annotations
of the statefulset.

- e2e/prometheus: Check how often resources (Secret, ConfigMap,
Prometheus CRD, Service) are updated to enforce that Prometheus Operator
only updated created resources if necessary.

- contrib/prometheus-config-reloader: Remove logic to retriev K8s
ConfigMaps. These are mounted into the pod right away now.

According to the man pages of `rm` and the `-f` option:
> Attempt to remove the files without prompting for confirma- tion,
> regardless of the file's permissions.  If the file does not exist, do
> not display a diagnostic message or modify the exit status to reflect an
> error.  The -f option overrides any previous -i options.

This patch prevents the `build.sh` script from failing if files do not
exist when attempting to delete them.

* kube-prometheus: fix alert rule K8SManyNodesNotReady

* fix alert "K8SManyNodesNotReady" in helm templates & make generate

* Use sync_kube_prometheus.py to make rules in helm in sync