test: use sleepy wait-for-log in reindex readonly

Also rename the busy wait-for-log method to prevent recurrence

test/functional/feature_reindex_readonly.py

@@ -75,7 +75,7 @@ class BlockstoreReindexTest(BitcoinTestFramework):
 
         if undo_immutable:
             self.log.debug("Attempt to restart and reindex the node with the unwritable block file")
-            with self.nodes[0].wait_for_debug_log([b"Reindexing finished"]):
+            with self.nodes[0].assert_debug_log(["Reindexing finished"], timeout=60):
                 self.start_node(0, extra_args=['-reindex', '-fastprune'])
             assert block_count == self.nodes[0].getblockcount()
             undo_immutable()