[autotest] Make (un)stable_test into properties

BUG=None
TEST=None

Change-Id: Ifcef6b68ae5a28d69564bb99fb56324aae4b5cb4
Reviewed-on: https://chromium-review.googlesource.com/419104
Commit-Ready: Allen Li <ayatane@chromium.org>
Tested-by: Allen Li <ayatane@chromium.org>
Reviewed-by: Richard Barnette <jrbarnette@google.com>
diff --git a/site_utils/suite_enumerator.py b/site_utils/suite_enumerator.py
index 6d2e4cb..6e613ea 100755
--- a/site_utils/suite_enumerator.py
+++ b/site_utils/suite_enumerator.py
@@ -73,10 +73,10 @@
     # name that appears in test.path
     PRETEST_LIST = ['firmware_FAFTSetup',]
     for test in filter(lambda test: test.name in \
-                              PRETEST_LIST, suite.stable_tests()):
+                              PRETEST_LIST, suite.stable_tests):
         print test.path
     for test in filter(lambda test: test.name not in \
-                       PRETEST_LIST, suite.stable_tests()):
+                       PRETEST_LIST, suite.stable_tests):
         print test.path
 
     # Check if test_suites/control.suite_name exists.