Enforcing gofmt -s on linter check (#1820)

This fix enforces gofmt -s on linter check in Makefile,
and fixes `plugin/kubernetes/handler_test.go` and
`plugin/tls/tls_test.go` with `gofmt -s`

Makefile

@@ -81,7 +81,7 @@ pb:
 linter:
 	go get -u github.com/alecthomas/gometalinter
 	gometalinter --install golint
-	gometalinter --deadline=2m --disable-all --enable=golint --enable=vet --vendor --exclude=^pb/ ./...
+	gometalinter --deadline=2m --disable-all --enable=gofmt --enable=golint --enable=vet --vendor --exclude=^pb/ ./...
 
 .PHONY: goimports
 goimports:

plugin/kubernetes/handler_test.go

@@ -137,7 +137,6 @@ var dnsTestCases = []test.Case{
 			test.AAAA("5678-abcd--2.hdls1.testns.svc.cluster.local.	5	IN	AAAA	5678:abcd::2"),
 			test.A("dup-name.hdls1.testns.svc.cluster.local.	5	IN	A	172.0.0.4"),
 			test.A("dup-name.hdls1.testns.svc.cluster.local.	5	IN	A	172.0.0.5"),
-
 		},
 	},
 	// AAAA