Drop deprecated metric to fix failing test.

Dropped via https://github.com/kubernetes/kubernetes/pull/103793

Signed-off-by: Damien Grisonnet <dgrisonn@redhat.com>

kube-apiserver has a histogram etcd_request_duration_seconds that
measures latency between the kube-apiserver and etcd instance.
This metrics is currently dropped by cluster-prometheus. Enable
this metrics so we have visibility into etcd latency.

We ensured that this does not enable other unwanted metrcis

count by(name) ({name=~"etcd_request.+"})

etcd_request_duration_seconds_bucket
etcd_request_duration_seconds_count
etcd_request_duration_seconds_sum

Starting with Kubernetes 1.6 `kubectl apply` works for TPRs so we can
start using it, therefore using multiple files is no issue.