backend: refactor backend Connections and HasAtomicReplace into Properties

internal/backend/retry/backend_retry.go

@@ -166,7 +166,7 @@ func (be *Backend) Save(ctx context.Context, h backend.Handle, rd backend.Rewind
 			return nil
 		}
 
-		if be.Backend.HasAtomicReplace() {
+		if be.Backend.Properties().HasAtomicReplace {
 			debug.Log("Save(%v) failed with error: %v", h, err)
 			// there is no need to remove files from backends which can atomically replace files
 			// in fact if something goes wrong at the backend side the delete operation might delete the wrong instance of the file

internal/backend/retry/backend_retry_test.go

@@ -69,7 +69,12 @@ func TestBackendSaveRetryAtomic(t *testing.T) {
 			calledRemove = true
 			return nil
 		},
-		HasAtomicReplaceFn: func() bool { return true },
+		PropertiesFn: func() backend.Properties {
+			return backend.Properties{
+				Connections:      2,
+				HasAtomicReplace: true,
+			}
+		},
 	}
 
 	TestFastRetries(t)