*: tests: Always set logger.disabled = False for consistency

See previous commit for context: which had to fix
commit_from_wrong_partition this way because without `logger.disabled =
False` logging could not produce its output under Python 3.6.

Discussion1: #360 (review)
Discussion2: #360 (comment)

src/ZODB/FileStorage/iterator.test

@@ -49,7 +49,9 @@ logging:
 
     >>> import logging, sys
     >>> old_log_level = logging.getLogger().getEffectiveLevel()
+    >>> old_log_disabled = logging.getLogger().disabled
     >>> logging.getLogger().setLevel(logging.DEBUG)
+    >>> logging.getLogger().disabled = False
     >>> handler = logging.StreamHandler(sys.stdout)
     >>> logging.getLogger().addHandler(handler)
 
@@ -144,6 +146,7 @@ starting point, or just pick up where another iterator left off:
     >>> it.close()
 
     >>> logging.getLogger().setLevel(old_log_level)
+    >>> logging.getLogger().disabled = old_log_disabled
     >>> logging.getLogger().removeHandler(handler)
 
 

src/ZODB/FileStorage/tests.py

@@ -176,6 +176,8 @@ def _save_index():
     >>> logger = logging.getLogger('ZODB.FileStorage')
     >>> logger.setLevel(logging.DEBUG)
     >>> logger.addHandler(handler)
+    >>> log_disabled = logger.disabled
+    >>> logger.disabled = False
     >>> index, pos, tid = fs._restore_index()
     >>> index.items() == fs._index.items()
     True
@@ -186,6 +188,7 @@ def _save_index():
     >>> fs.close()
     >>> logger.setLevel(logging.NOTSET)
     >>> logger.removeHandler(handler)
+    >>> logger.disabled = log_disabled
     >>> sys.setrecursionlimit(old_limit)
 
     """

src/ZODB/tests/loggingsupport.py

@@ -83,6 +83,7 @@ def __init__(self, *names, **kw):
     def setLoggerLevel(self, level=1):
         self.level = level
         self.oldlevels = {}
+        self.olddisabled = {}
 
     def emit(self, record):
         self.records.append(record)
@@ -94,13 +95,16 @@ def install(self):
         for name in self.names:
             logger = logging.getLogger(name)
             self.oldlevels[name] = logger.level
+            self.olddisabled[name] = logger.disabled
             logger.setLevel(self.level)
+            logger.disabled = False
             logger.addHandler(self)
 
     def uninstall(self):
         for name in self.names:
             logger = logging.getLogger(name)
             logger.setLevel(self.oldlevels[name])
+            logger.disabled = self.olddisabled[name]
             logger.removeHandler(self)
 
     def __str__(self):