[#959] node: Set mode to shard's components when open it

Avoid opening database for `metabase` and `cache` in `Degraded` mode.

Signed-off-by: Anton Nikiforov <an.nikiforov@yadro.com>

pkg/local_object_storage/writecache/mode_test.go

@@ -0,0 +1,30 @@
+package writecache
+
+import (
+	"context"
+	"testing"
+
+	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/shard/mode"
+	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/util/logger/test"
+	"github.com/stretchr/testify/require"
+)
+
+func TestMode(t *testing.T) {
+	t.Parallel()
+	wc := New(
+		WithLogger(test.NewLogger(t)),
+		WithFlushWorkersCount(2),
+		WithPath(t.TempDir()))
+
+	require.NoError(t, wc.Open(context.Background(), mode.DegradedReadOnly))
+	require.Nil(t, wc.(*cache).db)
+	require.NoError(t, wc.Init())
+	require.Nil(t, wc.(*cache).db)
+	require.NoError(t, wc.Close())
+
+	require.NoError(t, wc.Open(context.Background(), mode.Degraded))
+	require.Nil(t, wc.(*cache).db)
+	require.NoError(t, wc.Init())
+	require.Nil(t, wc.(*cache).db)
+	require.NoError(t, wc.Close())
+}