Replace freeport with independent impl. (elastic#7853)

This removes a trivial dep I recently added and substitutes it for a small function.

NOTICE.txt

@@ -1718,28 +1718,6 @@ For more information, please see http://www.bis.doc.gov
 
 See also http://www.apache.org/dev/crypto.html and/or seek legal counsel.
 
---------------------------------------------------------------------
-Dependency: github.com/phayes/freeport
-Revision: e27662a4a9d6b2083dfd7e7b5d0e30985daca925
-License type (autodetected): BSD-3-Clause
-./vendor/github.com/phayes/freeport/LICENSE.md:
---------------------------------------------------------------------
-Open Source License (BSD 3-Clause)
-----------------------------------
-
-Copyright (c) 2014, Patrick Hayes / HighWire Press
-All rights reserved.
-
-Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
-
-1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
-
-2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
-
-3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.
-
-THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-
 --------------------------------------------------------------------
 Dependency: github.com/pierrec/lz4
 Revision: 90290f74b1b4d9c097f0a3b3c7eba2ef3875c699

heartbeat/monitors/active/http/http_test.go

@@ -25,13 +25,12 @@ import (
 
 	"github.com/stretchr/testify/require"
 
-	"github.com/phayes/freeport"
-
 	"github.com/elastic/beats/heartbeat/hbtest"
 	"github.com/elastic/beats/heartbeat/monitors"
 	"github.com/elastic/beats/libbeat/beat"
 	"github.com/elastic/beats/libbeat/common"
 	"github.com/elastic/beats/libbeat/common/mapval"
+	btesting "github.com/elastic/beats/libbeat/testing"
 	"github.com/elastic/beats/libbeat/testing/mapvaltest"
 )
 
@@ -198,7 +197,9 @@ func TestDownStatuses(t *testing.T) {
 
 func TestConnRefusedJob(t *testing.T) {
 	ip := "127.0.0.1"
-	port := uint16(freeport.GetPort())
+	port, err := btesting.AvailableTCP4Port()
+	require.NoError(t, err)
+
 	url := fmt.Sprintf("http://%s:%d", ip, port)
 
 	event := testRequest(t, url)

heartbeat/monitors/active/tcp/tcp_test.go

@@ -24,15 +24,14 @@ import (
 
 	"github.com/stretchr/testify/require"
 
-	"github.com/phayes/freeport"
-
 	"net/http"
 
 	"github.com/elastic/beats/heartbeat/hbtest"
 	"github.com/elastic/beats/heartbeat/monitors"
 	"github.com/elastic/beats/libbeat/beat"
 	"github.com/elastic/beats/libbeat/common"
 	"github.com/elastic/beats/libbeat/common/mapval"
+	btesting "github.com/elastic/beats/libbeat/testing"
 	"github.com/elastic/beats/libbeat/testing/mapvaltest"
 )
 
@@ -91,7 +90,9 @@ func TestUpEndpointJob(t *testing.T) {
 
 func TestConnectionRefusedEndpointJob(t *testing.T) {
 	ip := "127.0.0.1"
-	port := uint16(freeport.GetPort())
+	port, err := btesting.AvailableTCP4Port()
+	require.NoError(t, err)
+
 	event := testTCPCheck(t, ip, port)
 
 	dialErr := fmt.Sprintf("dial tcp %s:%d", ip, port)

libbeat/testing/available_port.go

@@ -0,0 +1,38 @@
+// Licensed to Elasticsearch B.V. under one or more contributor
+// license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright
+// ownership. Elasticsearch B.V. licenses this file to you under
+// the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+package testing
+
+import "net"
+
+// AvailableTCP4Port returns an unused TCP port for 127.0.0.1.
+func AvailableTCP4Port() (uint16, error) {
+	resolved, err := net.ResolveTCPAddr("tcp4", "127.0.0.1:0")
+	if err != nil {
+		return 0, err
+	}
+
+	listener, err := net.ListenTCP("tcp4", resolved)
+	if err != nil {
+		return 0, err
+	}
+	defer listener.Close()
+
+	tcpAddr := uint16(listener.Addr().(*net.TCPAddr).Port)
+
+	return tcpAddr, nil
+}

vendor/vendor.json

@@ -1252,12 +1252,6 @@
 			"revision": "653207bc29a6d2d62b5d4f55b596467cb715a128",
 			"revisionTime": "2017-03-27T18:58:03Z"
 		},
-		{
-			"checksumSHA1": "kZRhErakejBG0U2e8D+Ap/Djje8=",
-			"path": "github.com/phayes/freeport",
-			"revision": "e27662a4a9d6b2083dfd7e7b5d0e30985daca925",
-			"revisionTime": "2017-10-02T18:52:19Z"
-		},
 		{
 			"checksumSHA1": "WmrPO1ovmQ7t7hs9yZGbr2SAoM4=",
 			"path": "github.com/pierrec/lz4",