test: create assert_not_equal util and add to where imports are needed

In the functional tests there are lots of cases where we assert != which
this new util will replace, we also are adding the imports and the new assertion

test/functional/feature_coinstatsindex.py

@@ -27,6 +27,7 @@ from test_framework.script import (
 )
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import (
+    assert_not_equal,
     assert_equal,
     assert_raises_rpc_error,
 )
@@ -275,12 +276,12 @@ class CoinStatsIndexTest(BitcoinTestFramework):
         res2 = index_node.gettxoutsetinfo(hash_type='muhash', hash_or_height=112)
         assert_equal(res["bestblock"], block)
         assert_equal(res["muhash"], res2["muhash"])
-        assert res["muhash"] != res_invalid["muhash"]
+        assert_not_equal(res["muhash"], res_invalid["muhash"])
 
         # Test that requesting reorged out block by hash is still returning correct results
         res_invalid2 = index_node.gettxoutsetinfo(hash_type='muhash', hash_or_height=reorg_block)
         assert_equal(res_invalid2["muhash"], res_invalid["muhash"])
-        assert res["muhash"] != res_invalid2["muhash"]
+        assert_not_equal(res["muhash"], res_invalid2["muhash"])
 
         # Add another block, so we don't depend on reconsiderblock remembering which
         # blocks were touched by invalidateblock