tests: System/compatibility tests for testing shim compatiblity (#1218)

Additional system tests for testing shim compatibility with the classic
client interface.

Also fixes a bug where encountering a retriable error after another
retriable error mid-stream raised an exception instead of retrying.

Fixes #1156

---------

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: gkevinzheng

google/cloud/bigtable/row_data.py

@@ -227,7 +227,7 @@ def _on_error(self, exc):
             retry_request = self._create_retry_request()
 
         self._row_merger = _RowMerger(self._row_merger.last_seen_row_key)
-        self.response_iterator = self.read_method(retry_request)
+        self.response_iterator = self.read_method(retry_request, retry=self.retry)
 
     def _read_next(self):
         """Helper for :meth:`__iter__`."""