switch to autox.py and robustify login/logout code

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
 
 
+class TimeoutError(error.TestError):
+    """Error raised when we time out when waiting on a condition."""
+
+
 def poll_for_condition(
-    condition, exception=None, timeout=10, sleep_interval=0.1):
+    condition, exception=None, timeout=10, sleep_interval=0.1, desc=None):
     """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
+    desc: description of default TimeoutError used if 'exception' is None
 
     Raises:
-        'exception' arg if supplied; error.TestError otherwise
+        'exception' arg if supplied; site_utils.TimeoutError 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')
+            if exception:
+                raise exception
+
+            if desc:
+                desc = 'Timed out waiting for condition: %s' % desc
+            else:
+                desc = 'Timed out waiting for unnamed condition'
+            raise error.TestError(desc)
+
         time.sleep(sleep_interval)