boskos: disable controller-runtime manager metrics

[ixdy]

The controller-runtime manager enables its own metrics serving by default on port 8080. This conflicts with the boskos server itself.

We probably don't need these metrics (at least not yet), so let's just disable them.

Follow-on to #16249.
x-ref #16267 (comment)

/assign @alvaroaleman @stevekuznetsov

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[alvaroaleman]

/lgtm

[alvaroaleman]

Interesting, I didn't notice this when I played around because the viper config reloading stuff seems to block forever when calling boskos with an empty config:

$ /tmp/boskos --namespace=default --log-level=debug -dynamic-resource-update-period=0 -kubeconfig=$KUBECONFIG -config="" 
{"component":"boskos","file":"/home/alvaro/git/work/test-infra/boskos/crds/client.go:134","func":"k8s.io/test-infra/boskos/crds.(*KubernetesClientOptions).CacheBackedClient","level":"info","msg":"Cache synced","sync-duration":"100.484959ms","time":"2020-02-13T09:07:27+01:00"}
{"component":"boskos","file":"/home/alvaro/git/work/test-infra/boskos/cmd/boskos/boskos.go:103","func":"main.main","level":"info","msg":"Created storage","time":"2020-02-13T09:07:27+01:00"}
2020/02/13 09:07:27 error: Config File "config" Not Found in "[]"