Refactor firewall reconcile.

[Gerrit91]

• Adapts to latest controller implementations of other extension providers (controller-library was not yet introduced, will be done for Gardener >=v1.5 controller)
• Smaller functions for firewall reconcile
• Compares firewall image properly and recreates firewall if image changed on shoot spec (respects semantic versioning)
• Fixes a possible issue where a firewall could be deleted even if it does not belong to the cluster anymore

[Gerrit91]

I tried it out and it is working nicely. We can now do these kind of things as well:

$ c cluster update f960732b-9562-4ef8-b488-8d5fb8a99104 --firewallimage firewall-ubuntu-2.0

And it will result into:

...
gardener-extension-provider-metal-58fdf74dc4-wp2js gardener-extension-provider-metal {"level":"info","ts":"2020-07-08T11:20:36.879Z","logger":"infrastructure-actuator","msg":"firewall image has changed","clusterid":"f960732b-9562-4ef8-b488-8d5fb8a99104","machineid":"00000000-0000-0000-0000-ac1f6b7befb4","current":"firewall-ubuntu-2.0.20200617","new":"firewall-ubuntu-2.0.20200701"}
...

[majst01]

Please update to the most recent version. Also here, we still refer to a ancient mcm:

github.com/gardener/machine-controller-manager => github.com/metal-pod/machine-controller-manager v0.0.0-20190801141331-4e2b75ebc6c0

This must be fixed as well