integration tests for several channel lifetime scenarios

* launches several Electrum components to interact on a regtest network
* reloads modules to remove side effects

synchronization of code is still TBD, get rid of asyncio.sleeps

electrum/lnworker.py

@@ -333,6 +333,7 @@ def start_network(self, network: 'Network'):
  async def stop(self):
  if self.listen_server:
  self.listen_server.close()
+ await self.listen_server.wait_closed()
  util.unregister_callback(self.on_proxy_changed)
  await self.taskgroup.cancel_remaining()
 
@@ -755,6 +756,7 @@ async def stop(self):
  self.stopping_soon = True
  if self.listen_server: # stop accepting new peers
  self.listen_server.close()
+ await self.listen_server.wait_closed()
  async with ignore_after(self.TIMEOUT_SHUTDOWN_FAIL_PENDING_HTLCS):
  await self.wait_for_received_pending_htlcs_to_get_removed()
  await LNWorker.stop(self)