Move several class definitions into try block

The class definitions are now able to be imported from the script.

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

Author: mulkieran

scripts/monitor_dbus_signals.py

@@ -427,8 +427,6 @@ def main():
     if __name__ == "__main__":
         main()
 
-except KeyboardInterrupt:
-
     class Diff:  # pylint: disable=too-few-public-methods
         """
         Diff between two different managed object results.
@@ -601,6 +599,8 @@ def __init__(self, object_path, interface_name):
         def __repr__(self):
             return f"MissingInterface({self.object_path!r}, {self.interface_name!r}"
 
+except KeyboardInterrupt:
+
     def _check_props(object_path, ifn, old_props, new_props):
         """
         Find differences between two sets of properties.