Restart buckd for any NailgunException
Restart buckd for any NailgunException

Summary:
I am sick of stuff like this...

```
2018-06-08 11:39:20,898 [ERROR][buck.py:232] Server disconnected unexpectedly: [Errno 104] Connection reset by peer
Traceback (most recent call last):
  File "programs/buck.py", line 201, in <module>
  File "programs/buck.py", line 188, in main
  File "programs/buck_tool.py", line 510, in launch_buck
    elif not self._is_buckd_running():
  File "programs/buck_tool.py", line 788, in _is_buckd_running
    c.send_command('ng-stats')
  File "pynailgun/ng.py", line 438, in send_command
    NailgunException.CONNECTION_BROKEN)
NailgunException: Server disconnected unexpectedly: [Errno 104] Connection reset by peer
```

If buckd feels like dropping a connection, fine, I'll just restart it.

Reviewed By: ttsugriy

fbshipit-source-id: 544605e

zpao/buck,Addepar/buck,brettwooldridge/buck,JoelMarcey/buck,brettwooldridge/buck,romanoid/buck,nguyentruongtho/buck,zpao/buck,romanoid/buck,romanoid/buck,romanoid/buck,zpao/buck,JoelMarcey/buck,SeleniumHQ/buck,nguyentruongtho/buck,facebook/buck,romanoid/buck,SeleniumHQ/buck,Addepar/buck,rmaz/buck,facebook/buck,rmaz/buck,rmaz/buck,JoelMarcey/buck,kageiit/buck,facebook/buck,SeleniumHQ/buck,nguyentruongtho/buck,kageiit/buck,shs96c/buck,SeleniumHQ/buck,JoelMarcey/buck,kageiit/buck,facebook/buck,brettwooldridge/buck,SeleniumHQ/buck,zpao/buck,shs96c/buck,shs96c/buck,romanoid/buck,JoelMarcey/buck,JoelMarcey/buck,Addepar/buck,rmaz/buck,zpao/buck,kageiit/buck,zpao/buck,brettwooldridge/buck,brettwooldridge/buck,JoelMarcey/buck,facebook/buck,nguyentruongtho/buck,shs96c/buck,brettwooldridge/buck,JoelMarcey/buck,SeleniumHQ/buck,kageiit/buck,shs96c/buck,Addepar/buck,rmaz/buck,shs96c/buck,kageiit/buck,facebook/buck,zpao/buck,Addepar/buck,Addepar/buck,rmaz/buck,Addepar/buck,SeleniumHQ/buck,brettwooldridge/buck,romanoid/buck,rmaz/buck,brettwooldridge/buck,romanoid/buck,kageiit/buck,JoelMarcey/buck,Addepar/buck,brettwooldridge/buck,rmaz/buck,romanoid/buck,SeleniumHQ/buck,JoelMarcey/buck,SeleniumHQ/buck,romanoid/buck,nguyentruongtho/buck,romanoid/buck,SeleniumHQ/buck,romanoid/buck,brettwooldridge/buck,shs96c/buck,Addepar/buck,SeleniumHQ/buck,nguyentruongtho/buck,nguyentruongtho/buck,shs96c/buck,SeleniumHQ/buck,SeleniumHQ/buck,brettwooldridge/buck,shs96c/buck,shs96c/buck,rmaz/buck,rmaz/buck,rmaz/buck,facebook/buck,shs96c/buck,romanoid/buck,shs96c/buck,shs96c/buck,rmaz/buck,JoelMarcey/buck,JoelMarcey/buck,brettwooldridge/buck,brettwooldridge/buck,Addepar/buck,JoelMarcey/buck,Addepar/buck,Addepar/buck,rmaz/buck,Addepar/buck