Fix probe test

Fix for a probe test that failed every once in a
while due to the early-majority change previously
committed. Sometimes a write would return success
before the third node had succeeded and the probe
test would look for on-disk evidence and fail,
when it would've been fine had it waited just a
bit longer for the third node to complete.

Since there's no real way for the probe test to
know when all three nodes are done, I just made
it retry once a second for several seconds before
reporting an error.

There may be more tests like this we'll have to
fix as we run across them.

Change-Id: I749e43d4580a7c726a9a8648f71bafefa70a05f5

test/probe/test_object_failures.py

@@ -14,6 +14,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import time
 from os import listdir, unlink
 from os.path import join as path_join
 from unittest import main, TestCase
@@ -27,8 +28,22 @@ from swift.obj.diskfile import write_metadata, read_metadata
 from test.probe.common import kill_servers, reset_environment
 
 
+RETRIES = 5
+
+
 def get_data_file_path(obj_dir):
-    files = sorted(listdir(obj_dir), reverse=True)
+    files = []
+    # We might need to try a few times if a request hasn't yet settled. For
+    # instance, a PUT can return success when just 2 of 3 nodes has completed.
+    for attempt in xrange(RETRIES + 1):
+        try:
+            files = sorted(listdir(obj_dir), reverse=True)
+            break
+        except Exception:
+            if attempt < RETRIES:
+                time.sleep(1)
+            else:
+                raise
     for filename in files:
         return path_join(obj_dir, filename)