layers: Add NotTestable to the ...stats.py script

Change-Id: I06befac273829cf54c1ba113be31da9ba3fee190
diff --git a/layers/vk_validation_stats.py b/layers/vk_validation_stats.py
index 21c0e0b..43f16a8 100755
--- a/layers/vk_validation_stats.py
+++ b/layers/vk_validation_stats.py
@@ -122,7 +122,7 @@
                     self.db_unimplemented_implicit.append(error_enum)
                 if implemented not in ['Y', 'N']:
                     self.db_invalid_implemented.append(error_enum)
-                if testname.lower() not in ['unknown', 'none']:
+                if testname.lower() not in ['unknown', 'none', 'nottestable']:
                     self.db_enum_to_tests[error_enum] = testname.split(',')
                     #if len(self.db_enum_to_tests[error_enum]) > 1:
                     #    print "Found check %s that has multiple tests: %s" % (error_enum, self.db_enum_to_tests[error_enum])