TUN-8427: Fix BackoffHandler's internally shared clock structure

A clock structure was used to help support unit testing timetravel
but it is a globally shared object and is likely unsafe to share
across tests. Reordering of the tests seemed to have intermittent
failures for the TestWaitForBackoffFallback specifically on windows
builds.

Adjusting this to be a shim inside the BackoffHandler struct should
resolve shared object overrides in unit testing.

Additionally, added the reset retries functionality to be inline with
the ResetNow function of the BackoffHandler to align better with
expected functionality of the method.

Removes unused reconnectCredentialManager.

retry/backoffhandler_test.go

@@ -13,10 +13,9 @@ func immediateTimeAfter(time.Duration) <-chan time.Time {
 }
 
 func TestBackoffRetries(t *testing.T) {
-	// make backoff return immediately
-	Clock.After = immediateTimeAfter
 	ctx := context.Background()
-	backoff := BackoffHandler{MaxRetries: 3}
+	// make backoff return immediately
+	backoff := BackoffHandler{maxRetries: 3, Clock: Clock{time.Now, immediateTimeAfter}}
 	if !backoff.Backoff(ctx) {
 		t.Fatalf("backoff failed immediately")
 	}
@@ -32,10 +31,10 @@ func TestBackoffRetries(t *testing.T) {
 }
 
 func TestBackoffCancel(t *testing.T) {
-	// prevent backoff from returning normally
-	Clock.After = func(time.Duration) <-chan time.Time { return make(chan time.Time) }
 	ctx, cancelFunc := context.WithCancel(context.Background())
-	backoff := BackoffHandler{MaxRetries: 3}
+	// prevent backoff from returning normally
+	after := func(time.Duration) <-chan time.Time { return make(chan time.Time) }
+	backoff := BackoffHandler{maxRetries: 3, Clock: Clock{time.Now, after}}
 	cancelFunc()
 	if backoff.Backoff(ctx) {
 		t.Fatalf("backoff allowed after cancel")
@@ -46,13 +45,12 @@ func TestBackoffCancel(t *testing.T) {
 }
 
 func TestBackoffGracePeriod(t *testing.T) {
+	ctx := context.Background()
 	currentTime := time.Now()
 	// make Clock.Now return whatever we like
-	Clock.Now = func() time.Time { return currentTime }
+	now := func() time.Time { return currentTime }
 	// make backoff return immediately
-	Clock.After = immediateTimeAfter
-	ctx := context.Background()
-	backoff := BackoffHandler{MaxRetries: 1}
+	backoff := BackoffHandler{maxRetries: 1, Clock: Clock{now, immediateTimeAfter}}
 	if !backoff.Backoff(ctx) {
 		t.Fatalf("backoff failed immediately")
 	}
@@ -70,10 +68,9 @@ func TestBackoffGracePeriod(t *testing.T) {
 }
 
 func TestGetMaxBackoffDurationRetries(t *testing.T) {
-	// make backoff return immediately
-	Clock.After = immediateTimeAfter
 	ctx := context.Background()
-	backoff := BackoffHandler{MaxRetries: 3}
+	// make backoff return immediately
+	backoff := BackoffHandler{maxRetries: 3, Clock: Clock{time.Now, immediateTimeAfter}}
 	if _, ok := backoff.GetMaxBackoffDuration(ctx); !ok {
 		t.Fatalf("backoff failed immediately")
 	}
@@ -95,10 +92,9 @@ func TestGetMaxBackoffDurationRetries(t *testing.T) {
 }
 
 func TestGetMaxBackoffDuration(t *testing.T) {
-	// make backoff return immediately
-	Clock.After = immediateTimeAfter
 	ctx := context.Background()
-	backoff := BackoffHandler{MaxRetries: 3}
+	// make backoff return immediately
+	backoff := BackoffHandler{maxRetries: 3, Clock: Clock{time.Now, immediateTimeAfter}}
 	if duration, ok := backoff.GetMaxBackoffDuration(ctx); !ok || duration > time.Second*2 {
 		t.Fatalf("backoff (%s) didn't return < 2 seconds on first retry", duration)
 	}
@@ -117,10 +113,9 @@ func TestGetMaxBackoffDuration(t *testing.T) {
 }
 
 func TestBackoffRetryForever(t *testing.T) {
-	// make backoff return immediately
-	Clock.After = immediateTimeAfter
 	ctx := context.Background()
-	backoff := BackoffHandler{MaxRetries: 3, RetryForever: true}
+	// make backoff return immediately
+	backoff := BackoffHandler{maxRetries: 3, retryForever: true, Clock: Clock{time.Now, immediateTimeAfter}}
 	if duration, ok := backoff.GetMaxBackoffDuration(ctx); !ok || duration > time.Second*2 {
 		t.Fatalf("backoff (%s) didn't return < 2 seconds on first retry", duration)
 	}