Make the scanner (become idle and) re-try sending messages to the controller when it fails
```
Jan 10 18:23:16 WARNING MainThread heartbeat.py:67 - print_heartbeat_message - There is no progress measuring new unique relays.
Jan 10 18:23:16 DEBUG MainThread scanner.py:548 - main_loop - Attempted to measure 317 relays in 7.899018947283427 minutes
Jan 10 18:23:16 CRITICAL MainThread scanner.py:707 - run_speedtest - Something went wrong.
Please create a ticket in https://trac.torproject.org with this traceback.
Jan 10 18:23:16 ERROR MainThread scanner.py:708 - run_speedtest -
Traceback (most recent call last):
File "/home/tom/sbws-venv/lib/python3.7/site-packages/sbws/core/scanner.py", line 700, in run_speedtest
max_pending_results, pool)
File "/home/tom/sbws-venv/lib/python3.7/site-packages/sbws/core/scanner.py", line 550, in main_loop
if controller.get_conf('TestingTorNetwork') == '1':
File "/home/tom/sbws-venv/lib/python3.7/site-packages/stem/control.py", line 2170, in get_conf
entries = self.get_conf_map(param, default, multiple)
File "/home/tom/sbws-venv/lib/python3.7/site-packages/stem/control.py", line 2254, in get_conf_map
response = self.msg('GETCONF %s' % ' '.join(lookup_params))
File "/home/tom/sbws-venv/lib/python3.7/site-packages/stem/control.py", line 651, in msg
self._socket.send(message)
File "/home/tom/sbws-venv/lib/python3.7/site-packages/stem/socket.py", line 450, in send
self._send(message, lambda s, sf, msg: send_message(sf, msg))
File "/home/tom/sbws-venv/lib/python3.7/site-packages/stem/socket.py", line 247, in _send
raise stem.SocketClosed()
stem.SocketClosed
```
It seems like sometimes tor does not respond to a controller message and that causes sbws to crash...
issue