Make mutating thread daemonic and stop it if there is an error in the

test thread.

Use with to simplify locking code.

src/ZEO/tests/invalidations_while_connecting.test

@@ -50,14 +50,12 @@ This tests tries to provoke this bug by:
     ...         i = random.randint(0, nobs-1)
     ...         if stop:
     ...             return
-    ...         lock.acquire()
-    ...         try:
+    ...         with lock:
     ...             conn2.root()[i].value += 1
     ...             tm.commit()
-    ...         finally:
-    ...             lock.release()
     ...         time.sleep(0)
     >>> thread = threading.Thread(target=run)
+    >>> thread.setDaemon(True)
     >>> thread.start()
 
 - restarting the first client, and
@@ -67,14 +65,14 @@ This tests tries to provoke this bug by:
     >>> handler = zope.testing.loggingsupport.InstalledHandler(
     ...    'ZEO', level=logging.ERROR)
 
-    >>> for c in range(10):
+    >>> try:
+    ...     for c in range(10):
     ...        time.sleep(.1)
     ...        db = ZODB.DB(ZEO.ClientStorage.ClientStorage(addr, client='x'))
-    ...    _ = lock.acquire()
-    ...    try:
-    ...      wait_until("connected and we've caught up",
-    ...                 lambda :
-    ...                    db.storage.is_connected()
+    ...        with lock:
+    ...            @wait_until("connected and we've caught up", timeout=199)
+    ...            def _():
+    ...                return (db.storage.is_connected()
     ...                        and db.storage.lastTransaction()
     ...                            == db.storage._server.lastTransaction()
     ...                        )
@@ -84,12 +82,11 @@ This tests tries to provoke this bug by:
     ...                if conn.root()[i].value != conn2.root()[i].value:
     ...                    print 'bad', c, i, conn.root()[i].value,
     ...                    print  conn2.root()[i].value
-    ...    finally:
-    ...      _ = lock.release()
     ...        db.close()
+    ... finally:
+    ...     stop = True
+    ...     thread.join(10)
 
-    >>> stop = True
-    >>> thread.join(10)
     >>> thread.isAlive()
     False