cmd/swarm, swarm/api/http, swarm/bmt, swarm/fuse, swarm/network/stream, swarm/storage, swarm/storage/encryption, swarm/testutil: use pseudo-random instead of crypto-random for test files content generation (#18083)

- Replace "crypto/rand" to "math/rand" for files content generation
- Remove swarm/network_test.go.Shuffle and swarm/btm/btm_test.go.Shuffle - because go1.9 support dropped (see https://github.com/ethereum/go-ethereum/pull/17807 and comments to swarm/network_test.go.Shuffle)

swarm/network/stream/intervals_test.go

@@ -18,10 +18,8 @@ package stream
 
 import (
 	"context"
-	crand "crypto/rand"
 	"encoding/binary"
 	"fmt"
-	"io"
 	"os"
 	"sync"
 	"testing"
@@ -36,6 +34,7 @@ import (
 	"github.com/ethereum/go-ethereum/swarm/network/simulation"
 	"github.com/ethereum/go-ethereum/swarm/state"
 	"github.com/ethereum/go-ethereum/swarm/storage"
+	"github.com/ethereum/go-ethereum/swarm/testutil"
 )
 
 func TestIntervalsLive(t *testing.T) {
@@ -130,7 +129,8 @@ func testIntervals(t *testing.T, live bool, history *Range, skipCheck bool) {
 		fileStore := item.(*storage.FileStore)
 
 		size := chunkCount * chunkSize
-		_, wait, err := fileStore.Store(ctx, io.LimitReader(crand.Reader, int64(size)), int64(size), false)
+
+		_, wait, err := fileStore.Store(ctx, testutil.RandomReader(1, size), int64(size), false)
 		if err != nil {
 			log.Error("Store error: %v", "err", err)
 			t.Fatal(err)