test: Always clear wait event in UntilEvent when it occurred.

So the instance is readily reusable and less likely to be misused.

caucase/test.py

@@ -182,16 +182,14 @@ class UntilEvent(object):
       raise ValueError # pragma: no cover
     self._action = value
 
-  def wait(self, timeout=10, clear=False):
+  def wait(self, timeout=10):
     """
     Wait for event to be waited upon at least once.
     timeout (float)
       Maximum number of seconds to wait for.
-    clear (bool)
-      Whether to reset this flag once reached.
     """
     result = self._wait_event.wait(timeout)
-    if result and clear:
+    if result:
       self._wait_event.clear()
     return result
 
@@ -1951,7 +1949,7 @@ class CaucaseTest(unittest.TestCase):
     updater_thread.daemon = True
     updater_thread.start()
     try:
-      self.assertTrue(until_updater.wait(clear=True))
+      self.assertTrue(until_updater.wait())
       # CSR must have been submitted
       csr_line_list = self._runClient(
         '--user-key', user_key_path,