Issue-3503: Improve timestamp validation in tests

CLITestCase.test_events_human_readable fails due to
 wrong assumption that host where tests were launched
 will have the same date time as Docker daemon.

 This fix introduces internal method for validating
 timestamp in Docker logs

Signed-off-by: Denys Makogon <lildee1991@gmail.com>

tests/acceptance/cli_test.py

@@ -1473,6 +1473,17 @@ class CLITestCase(DockerClientTestCase):
         assert Counter(e['action'] for e in lines) == {'create': 2, 'start': 2}
 
     def test_events_human_readable(self):
+
+        def has_timestamp(string):
+            str_iso_date, str_iso_time, container_info = string.split(' ', 2)
+            try:
+                return isinstance(datetime.datetime.strptime(
+                    '%s %s' % (str_iso_date, str_iso_time),
+                    '%Y-%m-%d %H:%M:%S.%f'),
+                    datetime.datetime)
+            except ValueError:
+                return False
+
         events_proc = start_process(self.base_dir, ['events'])
         self.dispatch(['up', '-d', 'simple'])
         wait_on_condition(ContainerCountCondition(self.project, 1))
@@ -1489,7 +1500,8 @@ class CLITestCase(DockerClientTestCase):
 
         assert expected_template.format('create', container.id) in lines[0]
         assert expected_template.format('start', container.id) in lines[1]
-        assert lines[0].startswith(datetime.date.today().isoformat())
+
+        assert has_timestamp(lines[0])
 
     def test_env_file_relative_to_compose_file(self):
         config_path = os.path.abspath('tests/fixtures/env-file/docker-compose.yml')