tests: maybe fix tearDown() issue in test_storage_upgrade.py

from travis logs:

--- Logging error ---

Traceback (most recent call last):
  File "/opt/python/3.7.6/lib/python3.7/logging/__init__.py", line 1028, in emit
    stream.write(msg + self.terminator)
ValueError: I/O operation on closed file.

Call stack:
  File "/opt/python/3.7.6/lib/python3.7/threading.py", line 890, in _bootstrap
    self._bootstrap_inner()
  File "/opt/python/3.7.6/lib/python3.7/threading.py", line 926, in _bootstrap_inner
    self.run()
  File "/home/travis/build/spesmilo/electrum/electrum/plugin.py", line 213, in run
    self.run_jobs()
  File "/home/travis/build/spesmilo/electrum/electrum/util.py", line 359, in on_stop
    self.logger.info("stopped")
Message: 'stopped'

electrum/tests/test_storage_upgrade.py

@@ -5,6 +5,7 @@ import json
 from typing import Optional
 import asyncio
 
+import electrum
 from electrum.wallet_db import WalletDB
 from electrum.wallet import Wallet
 from electrum import constants
@@ -312,6 +313,8 @@ class TestStorageUpgrade(WalletTestCase):
 
 ##########
 
+    plugins: 'electrum.plugin.Plugins'
+
     @classmethod
     def setUpClass(cls):
         super().setUpClass()
@@ -323,12 +326,14 @@ class TestStorageUpgrade(WalletTestCase):
 
         gui_name = 'cmdline'
         # TODO it's probably wasteful to load all plugins... only need Trezor
-        Plugins(config, gui_name)
+        cls.plugins = Plugins(config, gui_name)
 
     @classmethod
     def tearDownClass(cls):
         super().tearDownClass()
         shutil.rmtree(cls.__electrum_path)
+        cls.plugins.stop()
+        cls.plugins.stopped_event.wait()
 
     def _upgrade_storage(self, wallet_json, accounts=1) -> Optional[WalletDB]:
         if accounts == 1:
@@ -358,8 +363,8 @@ class TestStorageUpgrade(WalletTestCase):
     def _sanity_check_upgraded_db(self, db):
         self.assertFalse(db.requires_split())
         self.assertFalse(db.requires_upgrade())
-        w = Wallet(db, None, config=self.config)
-        w.stop()
+        wallet = Wallet(db, None, config=self.config)
+        asyncio.run_coroutine_threadsafe(wallet.stop(), self.asyncio_loop).result()
 
     @staticmethod
     def _load_db_from_json_string(*, wallet_json, manual_upgrades):

electrum/util.py

@@ -317,6 +317,7 @@ class DaemonThread(threading.Thread, Logger):
         self.running_lock = threading.Lock()
         self.job_lock = threading.Lock()
         self.jobs = []
+        self.stopped_event = threading.Event()  # set when fully stopped
 
     def add_jobs(self, jobs):
         with self.job_lock:
@@ -357,6 +358,7 @@ class DaemonThread(threading.Thread, Logger):
             jnius.detach()
             self.logger.info("jnius detach")
         self.logger.info("stopped")
+        self.stopped_event.set()
 
 
 def print_stderr(*args):