validation: allow trailing period in dns search

The trailing period tells the resolver to stop immediately instead
of trying recursively. With that said, trailing period should be
acceptable in searches.

pkg/apis/core/validation/validation.go

@@ -2695,6 +2695,10 @@ func validatePodDNSConfig(dnsConfig *core.PodDNSConfig, dnsPolicy *core.DNSPolic
 			allErrs = append(allErrs, field.Invalid(fldPath.Child("searches"), dnsConfig.Searches, "must not have more than 256 characters (including spaces) in the search list"))
 		}
 		for i, search := range dnsConfig.Searches {
+			// it is fine to have a trailing dot
+			if strings.HasSuffix(search, ".") {
+				search = search[0 : len(search)-1]
+			}
 			allErrs = append(allErrs, ValidateDNS1123Subdomain(search, fldPath.Child("searches").Index(i))...)
 		}
 		// Validate options.