UPSTREAM: <carry>: openshift: Vendor required modules

Update `go.mod`, `go.sum`, and `vendor/` after the
v1.8.1 rebase.

This commit picks up openshift/coredns-mdns#73
which migrates openshift/coredns-mdns to use coredns v1.8.1.

go.mod

@@ -6,30 +6,23 @@ require (
 	github.com/Azure/azure-sdk-for-go v40.6.0+incompatible
 	github.com/Azure/go-autorest/autorest v0.11.17
 	github.com/Azure/go-autorest/autorest/azure/auth v0.5.6
-	github.com/Azure/go-autorest/autorest/to v0.2.0 // indirect
-	github.com/DataDog/datadog-go v3.5.0+incompatible // indirect
 	github.com/aws/aws-sdk-go v1.36.28
 	github.com/coredns/caddy v1.1.0
 	github.com/dnstap/golang-dnstap v0.3.0
-	github.com/dustin/go-humanize v1.0.0 // indirect
 	github.com/farsightsec/golang-framestream v0.3.0
 	github.com/golang/protobuf v1.4.3
-	github.com/gorilla/websocket v1.4.0 // indirect
 	github.com/grpc-ecosystem/grpc-opentracing v0.0.0-20180507213350-8e809c8a8645
-	github.com/hashicorp/golang-lru v0.5.4 // indirect
-	github.com/imdario/mergo v0.3.9 // indirect
 	github.com/infobloxopen/go-trees v0.0.0-20190313150506-2af4e13f9062
 	github.com/matttproud/golang_protobuf_extensions v1.0.1
 	github.com/miekg/dns v1.1.35
+	github.com/openshift/coredns-mdns v0.0.0-20210224160723-223279380811
 	github.com/opentracing/opentracing-go v1.2.0
 	github.com/openzipkin-contrib/zipkin-go-opentracing v0.4.5
 	github.com/openzipkin/zipkin-go v0.2.2
-	github.com/philhofer/fwd v1.0.0 // indirect
 	github.com/prometheus/client_golang v1.9.0
 	github.com/prometheus/client_model v0.2.0
 	github.com/prometheus/common v0.15.0
 	go.etcd.io/etcd v0.5.0-alpha.5.0.20200306183522-221f0cc107cb
-	go.uber.org/zap v1.14.1 // indirect
 	golang.org/x/crypto v0.0.0-20201221181555-eec23a3978ad
 	golang.org/x/sys v0.0.0-20201214210602-f9fddec55a1e
 	google.golang.org/api v0.29.0