Set maxDiff to None for some TestCase subclasses

Omit the ones that don't run any tests but are just used for their setUp
and tearDown methods.

Signed-off-by: mulhern <amulhern@redhat.com>

Author: mulkieran

testlib/infra.py

@@ -238,6 +238,8 @@ class PoolMetadataMonitor(unittest.TestCase):
     Manage verification of consistency of pool-level metadata.
     """
 
+    maxDiff = None
+
     def _check_encryption_information_consistency(self, pool_object_path, metadata):
         """
         Check whether D-Bus and metadata agree about encryption state of pool.
@@ -302,6 +304,8 @@ class SysfsMonitor(unittest.TestCase):
     Manage verification of sysfs files for devices.
     """
 
+    maxDiff = None
+
     def run_check(self):
         """
         Run the check.
@@ -339,6 +343,8 @@ class SymlinkMonitor(unittest.TestCase):
     Manage verification of device symlinks.
     """
 
+    maxDiff = None
+
     def run_check(self):
         """
         Run the check.
@@ -361,6 +367,8 @@ class FilesystemSymlinkMonitor(unittest.TestCase):
     Verify that devicmapper devices for filesystems have corresponding symlinks.
     """
 
+    maxDiff = None
+
     def run_check(self, stop_time):
         """
         Check that the filesystem links on the D-Bus and the filesystem links
@@ -433,6 +441,8 @@ class DbusMonitor(unittest.TestCase):
     Manage starting and stopping the D-Bus monitor script.
     """
 
+    maxDiff = None
+
     def setUp(self):
         """
         Set up the D-Bus monitor for a test run.