Automatic merge from submit-queue (batch tested with PRs 45040, 48960)

Do not generate warning event on dns search deduplication

In the case that the node is able to use the cluster DNS, `cluster.local` will already be in the node search domains in `/etc/resolv.conf`.  The kubelet then parses `/etc/resolv.conf` on the node and combines it with  $namespace.svc.$clusterDomain, svc.$clusterDomain, and $clusterDomain to create the pod DNS search domains.  clusterDomain is `cluster.local` by default.  This causes the code to generate a Warning event visible to the user for _every_ pod:

```
Warning   DNSSearchForming     Found and omitted duplicated dns domain in host search line: 'cluster.local' during merging with cluster dns domains
```
This is really overkill.  IMHO, this should be done in the background with no user level notification or logging at all.

xref https://bugzilla.redhat.com/show_bug.cgi?id=1471198

@derekwaynecarr @eparis @vefimova