[qa] Improve sync_blocks error messages.

qa/rpc-tests/test_framework/util.py

@@ -132,10 +132,12 @@ def sync_blocks(rpc_connections, *, wait=1, timeout=60):
         if tips == [tips[0]] * len(tips):
             return
         if heights == [heights[0]] * len(heights):
-            raise AssertionError("Block sync failed: (Hashes don't match)")
+            raise AssertionError("Block sync failed, mismatched block hashes:{}".format(
+                                 "".join("\n  {!r}".format(tip) for tip in tips)))
         timeout -= wait
         maxheight = max(heights)
-    raise AssertionError("Block sync failed with heights: {}".format(heights))
+    raise AssertionError("Block sync to height {} timed out:{}".format(
+                         maxheight, "".join("\n  {!r}".format(tip) for tip in tips)))
 
 def sync_chain(rpc_connections, *, wait=1, timeout=60):
     """