testing: replace @flaky with @pytest.mark.flaky [(#3496)](GoogleCloudPlatform/python-docs-samples#3496)

* testing: replace @flaky with @pytest.mark.flaky

* lint

* mark few tests as flaky

that involves LRO polling.

* lint

Author: Takashi Matsuo

samples/snippets/v3/api-client/list_resources_test.py

@@ -23,7 +23,6 @@
 import os
 import re
 
-from flaky import flaky
 import googleapiclient.discovery
 import pytest
 
@@ -38,7 +37,7 @@ def client():
     return googleapiclient.discovery.build('monitoring', 'v3')
 
 
-@flaky
+@pytest.mark.flaky
 def test_list_monitored_resources(client, capsys):
     PROJECT_RESOURCE = "projects/{}".format(PROJECT)
     list_resources.list_monitored_resource_descriptors(
@@ -49,7 +48,7 @@ def test_list_monitored_resources(client, capsys):
     assert regex.search(stdout) is not None
 
 
-@flaky
+@pytest.mark.flaky
 def test_list_metrics(client, capsys):
     PROJECT_RESOURCE = "projects/{}".format(PROJECT)
     list_resources.list_metric_descriptors(
@@ -60,7 +59,7 @@ def test_list_metrics(client, capsys):
     assert regex.search(stdout) is not None
 
 
-@flaky
+@pytest.mark.flaky
 def test_list_timeseries(client, capsys):
     PROJECT_RESOURCE = "projects/{}".format(PROJECT)
     list_resources.list_timeseries(