**Apache Airflow version**: 2.1.0


**Environment**:

- **Cloud provider or hardware configuration**:
- **OS** (e.g. from /etc/os-release):
- **Kernel** (e.g. `uname -a`):
- **Install tools**:
- **Others**:

**What happened**:  FileSensor does not recognize directories with wildcard glob matching.

**What you expected to happen**: FileSensor would sense a directory that contains files if it matches with the wild card option.

**How to reproduce it**: Create a directory with a pattern that matches a wild card using glob



**Anything else we need to know**: Code from FileSensor source that I believe to cause the issue:

```
for path in glob(full_path):
            if os.path.isfile(path):
                mod_time = os.path.getmtime(path)
                mod_time = datetime.datetime.fromtimestamp(mod_time).strftime('%Y%m%d%H%M%S')
                self.log.info('Found File %s last modified: %s', str(path), str(mod_time))
                return True

            for _, _, files in os.walk(full_path):
                if len(files) > 0:
                    return True
        return False

```
I believe to resolve the issue `full_path` in os.walk should be `path` instead.


tests/sensors/test_filesystem.py
#
#
#
#
import os.path
import shutil
import tempfile
import unittest
import pytest
from airflow.exceptions import AirflowSensorTimeout
from airflow.models.dag import DAG
from airflow.sensors.filesystem import FileSensor
from airflow.utils.timezone import datetime
TEST_DAG_ID = 'unit_tests_file_sensor'
DEFAULT_DATE = datetime(2015, 1, 1)
class TestFileSensor(unittest.TestCase):
    def setUp(self):
        from airflow.hooks.filesystem import FSHook
        hook = FSHook()
        args = {'owner': 'airflow', 'start_date': DEFAULT_DATE}
        dag = DAG(TEST_DAG_ID + 'test_schedule_dag_once', default_args=args)
        self.hook = hook
        self.dag = dag
    def test_simple(self):