[jjo] add kube-router support (#3339)

* [jjo] add kube-router support

Fixes cloudnativelabs/kube-router#147.

* add kube-router as another network_plugin choice
* support most used kube-router flags via
  `kube_router_foo` vars as other plugins
* implement replacing kube-proxy (--run-service-proxy=true) via
  `kube_proxy_mode: none`, verified in a _non kubeadm_enabled_
  install, should also work for recent kubeadm releases via
  `skipKubeProxyInstall: true` config

* [jjo] address PR#3339 review from @woopstar

* add busybox image used by kube-router to downloads

* fix busybox download groups key

* rework kubeadm_enabled + kube_router_run_service_proxy

- verify it working ok w/the kubeadm_enabled and
  kube_router_run_service_proxy true or false

- introduce `kube_proxy_remove` fact, to decouple logic
  from kube_proxy_mode (which affects kubeadm configmap
  settings, thus no-good to ab-use it to 'none')

* improve kube-router.md re: kubeadm_enabled and kube_router_run_service_proxy

* address @woopstar latest review

* add inventory/sample/group_vars/k8s-cluster/k8s-net-kube-router.yml

* fix kube_router_run_service_proxy conditional for kube-proxy removal

* fix kube_proxy_remove fact (w/ |bool), add some needed kube-proxy tags on my and existing changes

* update kube-router tolerations for 1.12 compatibility

* add PriorityClass to kube-router DaemonSet

README.md

@@ -117,6 +117,7 @@ Supported Components
     -   [contiv](https://github.com/contiv/install) v1.1.7
     -   [flanneld](https://github.com/coreos/flannel) v0.10.0
     -   [weave](https://github.com/weaveworks/weave) v2.4.1
+    -   [kube-router](https://github.com/cloudnativelabs/kube-router) v0.2.0
 -   Application
     -   [cephfs-provisioner](https://github.com/kubernetes-incubator/external-storage) v2.1.0-k8s1.11
     -   [cert-manager](https://github.com/jetstack/cert-manager) v0.5.0
@@ -164,6 +165,11 @@ You can choose between 6 network plugins. (default: `calico`, except Vagrant use
 -   [weave](docs/weave.md): Weave is a lightweight container overlay network that doesn't require an external K/V database cluster.
     (Please refer to `weave` [troubleshooting documentation](http://docs.weave.works/weave/latest_release/troubleshooting.html)).
 
+-   [kube-router](doc/kube-router.md): Kube-router is a L3 CNI for Kubernetes networking aiming to provide operational
+    simplicity and high performance: it uses IPVS to provide Kube Services Proxy (if setup to replace kube-proxy),
+    iptables for network policies, and BGP for ods L3 networking (with optionally BGP peering with out-of-cluster BGP peers).
+    It can also optionally advertise routes to Kubernetes cluster Pods CIDRs, ClusterIPs, ExternalIPs and LoadBalancerIPs.
+
 The choice is defined with the variable `kube_network_plugin`. There is also an
 option to leverage built-in cloud provider networking instead.
 See also [Network checker](docs/netcheck.md).