Pull request: all: update go and backend tools

Closes #2576.
Updates #2275.
Updates #2419.
Updates #2443.

Squashed commit of the following:

commit b1a4809ada298d675de12740051ba26fb9945957
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Fri May 21 14:01:40 2021 +0300

    all: add --local-frontend, upd docker

commit 619ee7c82f27e3405753003dbec556ffb056d025
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Thu May 20 15:02:33 2021 +0300

    bamboo-specs: bump docker version

commit 5c2b2fbce80afdcc81fd0cb83674dc3d64facbf1
Merge: 6536b32d 9c60aef6
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Thu May 20 15:01:47 2021 +0300

    Merge branch 'master' into 2275-upd-go

commit 6536b32dd4580425f7dedde6765463a79b9bd699
Merge: 9bb32bc4 6f7fd33a
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed May 19 20:38:48 2021 +0300

    Merge branch 'master' into 2275-upd-go

commit 9bb32bc4c0ac0f3a97195adc75359e48c9c58897
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed May 19 18:48:50 2021 +0300

    all: fix build, imp err handling

commit 6868eac7f7d2980fb706881f53e72afe5f7c3447
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed May 19 18:09:32 2021 +0300

    all: fix github lint

commit ebbb9c55f32fbd57e34e8b161016aa6b291c097c
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed May 19 17:36:56 2021 +0300

    all: update go and backend tools

internal/aghnet/etchostscontainer.go

@@ -4,7 +4,6 @@ import (
 	"bufio"
 	"errors"
 	"io"
-	"io/ioutil"
 	"net"
 	"os"
 	"path/filepath"
@@ -345,7 +344,7 @@ func (ehc *EtcHostsContainer) updateHosts() {
 	ehc.load(table, tableRev, ehc.hostsFn)
 
 	for _, dir := range ehc.hostsDirs {
-		fis, err := ioutil.ReadDir(dir)
+		des, err := os.ReadDir(dir)
 		if err != nil {
 			if !errors.Is(err, os.ErrNotExist) {
 				log.Error("etchostscontainer: Opening directory: %q: %s", dir, err)
@@ -354,8 +353,8 @@ func (ehc *EtcHostsContainer) updateHosts() {
 			continue
 		}
 
-		for _, fi := range fis {
-			ehc.load(table, tableRev, filepath.Join(dir, fi.Name()))
+		for _, de := range des {
+			ehc.load(table, tableRev, filepath.Join(dir, de.Name()))
 		}
 	}
 

internal/aghnet/etshostscontainer_test.go

@@ -1,7 +1,6 @@
 package aghnet
 
 import (
-	"io/ioutil"
 	"net"
 	"os"
 	"strings"
@@ -23,7 +22,7 @@ func prepareTestFile(t *testing.T) (f *os.File) {
 
 	dir := t.TempDir()
 
-	f, err := ioutil.TempFile(dir, "")
+	f, err := os.CreateTemp(dir, "")
 	require.Nil(t, err)
 	require.NotNil(t, f)
 	t.Cleanup(func() {

internal/aghnet/net_darwin.go

@@ -1,11 +1,13 @@
 // +build darwin
 
+//go:build darwin
+
 package aghnet
 
 import (
 	"errors"
 	"fmt"
-	"io/ioutil"
+	"os"
 	"regexp"
 	"strings"
 
@@ -140,7 +142,7 @@ func ifaceSetStaticIP(ifaceName string) (err error) {
 // getEtcResolvConfServers returns a list of nameservers configured in
 // /etc/resolv.conf.
 func getEtcResolvConfServers() ([]string, error) {
-	body, err := ioutil.ReadFile("/etc/resolv.conf")
+	body, err := os.ReadFile("/etc/resolv.conf")
 	if err != nil {
 		return nil, err
 	}

internal/aghnet/net_linux.go

@@ -1,5 +1,7 @@
 // +build linux
 
+//go:build linux
+
 package aghnet
 
 import (
@@ -7,7 +9,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net"
 	"os"
 	"strings"
@@ -139,7 +140,7 @@ func ifaceSetStaticIP(ifaceName string) (err error) {
 	gatewayIP := GatewayIP(ifaceName)
 	add := updateStaticIPdhcpcdConf(ifaceName, ipNet.String(), gatewayIP, ipNet.IP)
 
-	body, err := ioutil.ReadFile("/etc/dhcpcd.conf")
+	body, err := os.ReadFile("/etc/dhcpcd.conf")
 	if err != nil {
 		return err
 	}

internal/aghnet/net_linux_test.go

@@ -1,5 +1,7 @@
 // +build linux
 
+//go:build linux
+
 package aghnet
 
 import (

internal/aghnet/net_others.go

@@ -1,5 +1,7 @@
 // +build !linux,!darwin
 
+//go:build !(linux || darwin)
+
 package aghnet
 
 import (

internal/aghnet/systemresolvers_others.go

@@ -1,5 +1,7 @@
 // +build !windows
 
+//go:build !windows
+
 package aghnet
 
 import (

internal/aghnet/systemresolvers_others_test.go

@@ -1,5 +1,7 @@
 // +build !windows
 
+//go:build !windows
+
 package aghnet
 
 import (

internal/aghnet/systemresolvers_windows.go

@@ -1,5 +1,7 @@
 // +build windows
 
+//go:build windows
+
 package aghnet
 
 import (

internal/aghnet/systemresolvers_windows_test.go

@@ -1,5 +1,7 @@
 // +build windows
 
+//go:build windows
+
 package aghnet
 
 // TODO(e.burkov): Write tests for Windows implementation.