tests: Fix occasional data race (#11223)

CI tests could trigger a data race.

Servers are generally not expected to reinitialize, so tests could trigger data races when reinitializing and async operations are running.

We add the option to safely reset global vars instead of overwriting.

Fixes races like:

```
WARNING: DATA RACE
Read at 0x00000477ab18 by goroutine 1159:
  github.com/minio/minio/cmd.FileInfo.ToObjectInfo()
      /home/runner/work/minio/minio/cmd/erasure-metadata.go:105 +0x16d
  github.com/minio/minio/cmd.erasureObjects.putObject()
      /home/runner/work/minio/minio/cmd/erasure-object.go:748 +0x13f8
  github.com/minio/minio/cmd.(*erasureObjects).listPath.func3.2()
      /home/runner/work/minio/minio/cmd/metacache-set.go:682 +0x7d3
  github.com/minio/minio/cmd.newMetacacheBlockWriter.func1.2()
      /home/runner/work/minio/minio/cmd/metacache-stream.go:777 +0x1c4
  github.com/minio/minio/cmd.newMetacacheBlockWriter.func1()
      /home/runner/work/minio/minio/cmd/metacache-stream.go:806 +0x614

Previous write at 0x00000477ab18 by goroutine 1269:
  [failed to restore the stack]

Goroutine 1159 (running) created at:
  github.com/minio/minio/cmd.newMetacacheBlockWriter()
      /home/runner/work/minio/minio/cmd/metacache-stream.go:760 +0x112
  github.com/minio/minio/cmd.(*erasureObjects).listPath.func3()
      /home/runner/work/minio/minio/cmd/metacache-set.go:672 +0xe22

Goroutine 1269 (running) created at:
  testing.(*T).Run()
      /opt/hostedtoolcache/go/1.14.13/x64/src/testing/testing.go:1095 +0x537
  testing.runTests.func1()
      /opt/hostedtoolcache/go/1.14.13/x64/src/testing/testing.go:1339 +0xa6
  testing.tRunner()
      /opt/hostedtoolcache/go/1.14.13/x64/src/testing/testing.go:1050 +0x1eb
  testing.runTests()
      /opt/hostedtoolcache/go/1.14.13/x64/src/testing/testing.go:1337 +0x594
  testing.(*M).Run()
      /opt/hostedtoolcache/go/1.14.13/x64/src/testing/testing.go:1252 +0x2ff
  github.com/minio/minio/cmd.TestMain()
      /home/runner/work/minio/minio/cmd/test-utils_test.go:120 +0x44e
  main.main()
      _testmain.go:1408 +0x223
==================
==================
WARNING: DATA RACE
Read at 0x00000477aae8 by goroutine 1159:
  github.com/minio/minio/cmd.(*BucketVersioningSys).Enabled()
      /home/runner/work/minio/minio/cmd/bucket-versioning.go:26 +0x52
  github.com/minio/minio/cmd.FileInfo.ToObjectInfo()
      /home/runner/work/minio/minio/cmd/erasure-metadata.go:105 +0x197
  github.com/minio/minio/cmd.erasureObjects.putObject()
      /home/runner/work/minio/minio/cmd/erasure-object.go:748 +0x13f8
  github.com/minio/minio/cmd.(*erasureObjects).listPath.func3.2()
      /home/runner/work/minio/minio/cmd/metacache-set.go:682 +0x7d3
  github.com/minio/minio/cmd.newMetacacheBlockWriter.func1.2()
      /home/runner/work/minio/minio/cmd/metacache-stream.go:777 +0x1c4
  github.com/minio/minio/cmd.newMetacacheBlockWriter.func1()
      /home/runner/work/minio/minio/cmd/metacache-stream.go:806 +0x614

Previous write at 0x00000477aae8 by goroutine 1269:
  [failed to restore the stack]

Goroutine 1159 (running) created at:
  github.com/minio/minio/cmd.newMetacacheBlockWriter()
      /home/runner/work/minio/minio/cmd/metacache-stream.go:760 +0x112
  github.com/minio/minio/cmd.(*erasureObjects).listPath.func3()
      /home/runner/work/minio/minio/cmd/metacache-set.go:672 +0xe22

Goroutine 1269 (running) created at:
  testing.(*T).Run()
      /opt/hostedtoolcache/go/1.14.13/x64/src/testing/testing.go:1095 +0x537
  testing.runTests.func1()
      /opt/hostedtoolcache/go/1.14.13/x64/src/testing/testing.go:1339 +0xa6
  testing.tRunner()
      /opt/hostedtoolcache/go/1.14.13/x64/src/testing/testing.go:1050 +0x1eb
  testing.runTests()
      /opt/hostedtoolcache/go/1.14.13/x64/src/testing/testing.go:1337 +0x594
  testing.(*M).Run()
      /opt/hostedtoolcache/go/1.14.13/x64/src/testing/testing.go:1252 +0x2ff
  github.com/minio/minio/cmd.TestMain()
      /home/runner/work/minio/minio/cmd/test-utils_test.go:120 +0x44e
  main.main()
      _testmain.go:1408 +0x223
==================
```

cmd/bucket-metadata-sys.go

@@ -477,6 +477,15 @@ func (sys *BucketMetadataSys) load(ctx context.Context, buckets []BucketInfo, ob
 	}
 }
 
+// Reset the state of the BucketMetadataSys.
+func (sys *BucketMetadataSys) Reset() {
+	sys.Lock()
+	for k := range sys.metadataMap {
+		delete(sys.metadataMap, k)
+	}
+	sys.Unlock()
+}
+
 // NewBucketMetadataSys - creates new policy system.
 func NewBucketMetadataSys() *BucketMetadataSys {
 	return &BucketMetadataSys{

cmd/bucket-versioning.go

@@ -51,6 +51,11 @@ func (sys *BucketVersioningSys) Get(bucket string) (*versioning.Versioning, erro
 	return globalBucketMetadataSys.GetVersioningConfig(bucket)
 }
 
+// Reset BucketVersioningSys to initial state.
+func (sys *BucketVersioningSys) Reset() {
+	// There is currently no internal state.
+}
+
 // NewBucketVersioningSys - creates new versioning system.
 func NewBucketVersioningSys() *BucketVersioningSys {
 	return &BucketVersioningSys{}

cmd/server-main.go

@@ -183,7 +183,12 @@ func newAllSubsystems() {
 	globalNotificationSys = NewNotificationSys(globalEndpoints)
 
 	// Create new bucket metadata system.
-	globalBucketMetadataSys = NewBucketMetadataSys()
+	if globalBucketMetadataSys == nil {
+		globalBucketMetadataSys = NewBucketMetadataSys()
+	} else {
+		// Reinitialize safely when testing.
+		globalBucketMetadataSys.Reset()
+	}
 
 	// Create the bucket bandwidth monitor
 	globalBucketMonitor = bandwidth.NewMonitor(GlobalServiceDoneCh)
@@ -210,7 +215,11 @@ func newAllSubsystems() {
 	globalBucketQuotaSys = NewBucketQuotaSys()
 
 	// Create new bucket versioning subsystem
-	globalBucketVersioningSys = NewBucketVersioningSys()
+	if globalBucketVersioningSys == nil {
+		globalBucketVersioningSys = NewBucketVersioningSys()
+	} else {
+		globalBucketVersioningSys.Reset()
+	}
 
 	// Create new bucket replication subsytem
 	globalBucketTargetSys = NewBucketTargetSys()