test: Clean up site_login.py a bit.

client/bin/site_utils.py

+# Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import time
+from autotest_lib.client.common_lib import error
+
+
+def poll_for_condition(
+    condition, exception=None, timeout=10, sleep_interval=0.1):
+    """Poll until a condition becomes true.
+
+    condition: function taking no args and returning bool
+    exception: exception to throw if condition doesn't become true
+    timeout: maximum number of seconds to wait
+    sleep_interval: time to sleep between polls
+
+    Raises:
+        'exception' arg if supplied; error.TestError otherwise
+    """
+    start_time = time.time()
+    while True:
+        if condition():
+            return
+        if time.time() + sleep_interval - start_time > timeout:
+            raise exception if exception else error.TestError(
+                'Timed out waiting for condition')
+        time.sleep(sleep_interval)