dynamic partition update order is deterministic.

Use an OrderedDict.
Test: builds

Change-Id: Ic3782c1961f0c2a735540b054eb3cace720c50bd
diff --git a/tools/releasetools/common.py b/tools/releasetools/common.py
index de3e3b8..0415894 100644
--- a/tools/releasetools/common.py
+++ b/tools/releasetools/common.py
@@ -2226,7 +2226,7 @@
              collections.Counter(e.partition for e in block_diffs).items()
              if count > 1])
 
-    self._partition_updates = dict()
+    self._partition_updates = collections.OrderedDict()
 
     for p, block_diff in block_diff_dict.items():
       self._partition_updates[p] = DynamicPartitionUpdate()
@@ -2277,7 +2277,7 @@
       logger.info("Updating dynamic partitions %s",
                   self._partition_updates.keys())
 
-    self._group_updates = dict()
+    self._group_updates = collections.OrderedDict()
 
     for g in tgt_groups:
       self._group_updates[g] = DynamicGroupUpdate()