Add AttributeError handling when stopping.

[seanpianka]

Add AttributeError handling when calling Service.stop. I noticed that this issue occurs after attempting to initialize a webdriver.Chrome instance while 'chromedriver' is not in PATH.

Here is the aforementioned error:

Message: 'chromedriver' executable needs to be in PATH. Please see https://sites.google.com/a/chromium.org/chromedriver/home

And here is the aforementioned stacktrace:

Exception ignored in: <bound method Service.__del__ of <selenium.webdriver.chrome.service.Service object at 0x7fae11780a20>>
Traceback (most recent call last):
  File "/home/sean/.../lib/python3.6/site-packages/selenium/webdriver/common/service.py", line 176, in __del__
    self.stop()
  File "/home/sean/.../lib/python3.6/site-packages/selenium/webdriver/common/service.py", line 146, in stop
    if self.process is None:
AttributeError: 'Service' object has no attribute 'process'

The proposed changes should not introduce any adverse effects as it will handle similarly to a situation where self.process does exist.

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[cgoldberg]

+1

[seanpianka]

Why did handling an AttributeError cause normally-passing tests to fail? Is some functionality and/or testcases relying on this behavior to build/pass?

[seanpianka]

Further errors, described in the following stacktrace, likely bear similar root causes (chromedriver executable_path being supplied while it is not in PATH).

Exception ignored in: <bound method Service.__del__ of <selenium.webdriver.chrome.service.Service object at 0x7f5144f8da20>>
Traceback (most recent call last):
  File "/home/sean/.../lib/python3.6/site-packages/selenium/webdriver/common/service.py", line 173, in __del__
  File "/home/sean/.../lib/python3.6/site-packages/selenium/webdriver/common/service.py", line 149, in stop
  File "/home/sean/.../lib/python3.6/site-packages/selenium/webdriver/common/service.py", line 120, in send_remote_shutdown_command
ImportError: sys.meta_path is None, Python is likely shutting down