refactor: open boltdb only while using it (#1879)

* refactor: open boltdb only while using it

* patch

* Update handler_test.go

* Update handler_test.go

* Update handler_test.go

* Update handler.go

* timeout * 10

* pr feedback

* fixup

pkg/artifactcache/handler_test.go

@@ -25,7 +25,10 @@ func TestHandler(t *testing.T) {
 
 	defer func() {
 		t.Run("inpect db", func(t *testing.T) {
-			require.NoError(t, handler.db.Bolt().View(func(tx *bbolt.Tx) error {
+			db, err := handler.openDB()
+			require.NoError(t, err)
+			defer db.Close()
+			require.NoError(t, db.Bolt().View(func(tx *bbolt.Tx) error {
 				return tx.Bucket([]byte("Cache")).ForEach(func(k, v []byte) error {
 					t.Logf("%s: %s", k, v)
 					return nil
@@ -36,7 +39,6 @@ func TestHandler(t *testing.T) {
 			require.NoError(t, handler.Close())
 			assert.Nil(t, handler.server)
 			assert.Nil(t, handler.listener)
-			assert.Nil(t, handler.db)
 			_, err := http.Post(fmt.Sprintf("%s/caches/%d", base, 1), "", nil)
 			assert.Error(t, err)
 		})