Mac连接Android手机，使用airtest命令跑脚本，无法正确结束，一直停留在orientationWatcher has ended

**描述问题bug**
Mac连接Android手机，使用airtest命令跑脚本，命令无法正确结束，一直停留在orientationWatcher has ended
脚本应该是没问题的，同样的脚本，同样的手机，在windows上使用airtest命令是没问题的。
经过排查，发现只要初始化了poco就会引发此问题，不使用poco，命令可以正常结束。

```
/usr/local/lib/python3.7/site-packages/airtest/aircv/utils.py:51: DeprecationWarning: The binary mode of fromstring is deprecated, as it behaves surprisingly on unicode inputs. Use frombuffer instead
nparr = np.fromstring(pngstr, np.uint8)
======================================================================
ERROR: runTest (airtest.cli.runner.AirtestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/usr/local/lib/python3.7/site-packages/airtest/cli/runner.py", line 61, in runTest
exec(compile(code.encode("utf-8"), pyfilepath, 'exec'), self.scope)
File "/Users/ziroom/android/workspace/jenkins/workspace/Air_Test/logout.air/logout.py", line 16, in
cExit()
File "common.air/common.py", line 48, in cExit
sys.exit(0)
SystemExit: 0

----------------------------------------------------------------------
Ran 1 test in 68.981s

FAILED (errors=1)
[05:57:07][DEBUG] /usr/local/lib/python3.7/site-packages/airtest/core/android/static/adb/mac/adb -P 5037 -s 85GABMDV5ANR forward --remove tcp:12774
[05:57:07][DEBUG] /usr/local/lib/python3.7/site-packages/airtest/core/android/static/adb/mac/adb -P 5037 -s 85GABMDV5ANR forward --remove tcp:13748
[05:57:07][DEBUG] /usr/local/lib/python3.7/site-packages/airtest/core/android/static/adb/mac/adb -P 5037 -s 85GABMDV5ANR forward --remove tcp:13789
[05:57:07][DEBUG] /usr/local/lib/python3.7/site-packages/airtest/core/android/static/adb/mac/adb -P 5037 -s 85GABMDV5ANR forward --remove tcp:13407
[05:57:07][DEBUG] orientationWatcher has ended
```

**复现步骤**
1. 脚本添加poco = AndroidUiautomationPoco(use_airtest_input=True, screenshot_each_action=False)
2. airtest运行此脚本
3. airtest命令无法结束

**预期效果**
希望airtest命令可以结束

**相关截图**
无

**python 版本:** `python3.7.2`

**poco 版本:** `1.0.75`
**airtest 版本：** `1.0.26`

**设备:**
- 型号: [e.g. 魅族mx5]
- 系统: [e.g. Android 5.1]

**其他相关环境信息**
在mac osx上运行异常，在windows上正常。