Refactor embedded services to service interface and manager

[fzdarsky]

With #152 and #153 we've started restructuring MicroShift such that embedded services (etcd, kube-apiserver, etc.) have their logic self-contained (one file per service), conform to a common Service interface, and using a service manager to implement startup dependencies and cancellation consistently.

So far, only etcd and kube-apiserver have been migrated over. We need all other components to be migrated, too:

• kube-controller-manager
• kube-scheduler
• openshift-preparation (namespaces, SCCs, CRDs, etc.)
• openshift-apiserver
• openshift-controller-manager
• kubelet
• kubeproxy
• component-loader (see Optionally start OpenShift components #144)

Services can likely be migrated over one-by-one in multiple PRs / by multiple people.

[fzdarsky]

Note that some services currently hardcode the SIGTERM signal handler to the stop channel in the upstream code and that patches in /hack/patches patch out from our vendored packages. When refactoring kube-scheduler, kube-controller-manager, and klusterlet (following the example of kube-apiserver), please therefore ensure to test without those patches applied (see also #163).

[oglok]

I will work on porting the kube-scheduler to the new service manager framework.

[sallyom]

I'll work on porting kube-controller-manager let's see how far I get b4 PTO

[husky-parul]

I will work on porting the kube-scheduler to the new service manager framework.

Oh I assigned that to myself. I will un-assign myself. Feel free to take it #199

[fzdarsky]

Addressed by #199, #200, #201, #229, #239.