add write and read service test

visualdl/backend/python/test_read_service.py

+import summary
+import numpy as np
+import unittest
+import time
+
+
+class StorageTester(unittest.TestCase):
+    def test_storage(self):
+        summary.set_writable_storage("./tmp_dir")
+        time.sleep(5)
+        summary.stop_service()
+
+
+if __name__ == '__main__':
+    unittest.main()

visualdl/backend/python/test_write_service.py

+import summary
+import numpy as np
+import unittest
+import time
+
+
+class StorageTester(unittest.TestCase):
+    def test_read_storage(self):
+        summary.set_readable_storage("./tmp")
+        time.sleep(1)
+        scalar = summary.read_scalar('tag01')
+        time.sleep(5)
+        summary.stop_service()
+
+
+if __name__ == '__main__':
+    unittest.main()