Retry on conflict updating labels/annotations

We retry up to 10 times, with a delay of 500ms between attempts.

This is necessary because OpenShift itself may be updating the Build
object as well.

Add debug logging of the object before modification, for clarification
of why the object is changing.

Signed-off-by: Tim Waugh <twaugh@redhat.com>

osbs/core.py

@@ -69,6 +69,9 @@ def retry(*args, **kwargs):
                     raise
 
                 last_exception = ex
+            finally:
+                if attempt != 0:
+                    logger.debug("retry: succeeded on attempt %d", attempt + 1)
 
         raise last_exception or RuntimeError("operation not attempted")