Exclude wardmodem/task_loop_unittest.py from unittest_suite

These unittests currently take around 30s because they involve dispatching
events from an asynchronous event loop. Speeding up this particular unittest
module will likely not happen in the near future, so exclude them from scheduled
tests.

BUG=chromium:254030
TEST=From autotest/files/ run /utils/unittest_suite.py and verify that
wardmodem.task_loop_unittest.py is not run.

Change-Id: If314ed58dcc487b3ed52af6d37b1856771a32487
Reviewed-on: https://gerrit.chromium.org/gerrit/59948
Reviewed-by: Aviv Keshet <akeshet@chromium.org>
Commit-Queue: Prathmesh Prabhu <pprabhu@chromium.org>
Tested-by: Prathmesh Prabhu <pprabhu@chromium.org>
diff --git a/utils/unittest_suite.py b/utils/unittest_suite.py
index c47098e..a3ef751 100755
--- a/utils/unittest_suite.py
+++ b/utils/unittest_suite.py
@@ -78,6 +78,7 @@
     'auth_server_unittest.py',
     'base_barrier_unittest.py',
     'logging_manager_test.py',
+    'task_loop_unittest.py'  # crbug.com/254030
     ))