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_assumeutxo.py

@@ -35,6 +35,7 @@ from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import (
     assert_approx,
     assert_equal,
+    assert_not_equal,
     assert_raises_rpc_error,
     ensure_for,
     sha256sum_file,
@@ -475,7 +476,7 @@ class AssumeutxoTest(BitcoinTestFramework):
         assert_equal(
             dump_output4['txoutset_hash'],
             "8a1db0d6e958ce0d7c963bc6fc91ead596c027129bacec68acc40351037b09d7")
-        assert sha256sum_file(dump_output['path']) != sha256sum_file(dump_output4['path'])
+        assert_not_equal(sha256sum_file(dump_output['path']), sha256sum_file(dump_output4['path']))
 
         # Use a hash instead of a height
         prev_snap_hash = n0.getblockhash(prev_snap_height)