Avoid adding signal handlers to the event loop at connection

1. Because if someone runs pylibjuju in an off-main thread, then
add_signal_handler will (rightfully) complain (see issue #1010).

2. Pylibjuju as a library shouldn't enforce a certain way of handling
signals. Clients should install their handlers however they wanna
handle them.

Fixes #1010

Author: cderici

juju/client/connection.py

@@ -5,7 +5,6 @@
 import json
 import logging
 import ssl
-import signal
 import urllib.request
 import weakref
 from http.client import HTTPSConnection
@@ -425,10 +424,6 @@ def _exit_tasks():
             for task in jasyncio.all_tasks():
                 task.cancel()
 
-        loop = jasyncio.get_running_loop()
-        for sig in (signal.SIGINT, signal.SIGTERM):
-            loop.add_signal_handler(sig, _exit_tasks)
-
         return (await websockets.connect(
             url,
             ssl=self._get_ssl(cacert),
@@ -473,11 +468,6 @@ async def close(self, to_reconnect=False):
         if self.proxy is not None:
             self.proxy.close()
 
-        # Remove signal handlers
-        loop = jasyncio.get_running_loop()
-        for sig in (signal.SIGINT, signal.SIGTERM):
-            loop.remove_signal_handler(sig)
-
     async def _recv(self, request_id):
         if not self.is_open:
             raise websockets.exceptions.ConnectionClosed(0, 'websocket closed')