…e machines

7720d4f test: fix failure in feature_nulldummy.py on single-core machines (Sebastian Falbesoner)
646b388 test: refactor: use named args for block_submit in feature_nulldummy.py (Sebastian Falbesoner)

Pull request description:

  On single-core machines, executing the test `feature_nulldummy.py` results in the following assertion error:

  ```
      ...
      2021-08-18T15:37:58.805000Z TestFramework (INFO): Test 4: Non-NULLDUMMY base multisig transaction is invalid after activation
      2021-08-18T15:37:58.814000Z TestFramework (ERROR): Assertion failed
      Traceback (most recent call last):
        File "[...]/test/functional/test_framework/test_framework.py", line 131, in main
          self.run_test()
        File "[...]/test/functional/feature_nulldummy.py", line 107, in run_test
          self.block_submit(self.nodes[0], [test4tx], accept=False)
        File "[...]/test/functional/feature_nulldummy.py", line 134, in block_submit
          assert_equal(None if accept else 'block-validation-failed', node.submitblock(block.serialize().hex()))
        File "[...]/test/functional/test_framework/util.py", line 49, in assert_equal
          raise AssertionError("not(%s)" % " == ".join(str(arg) for arg in (thing1, thing2) + args))
      AssertionError: not(block-validation-failed == non-mandatory-script-verify-flag (Dummy CHECKMULTISIG argument must be zero))
      2021-08-18T15:37:58.866000Z TestFramework (INFO): Stopping nodes
      ...
  ```

  There are hardly any single-core machines around anymore, but the behaviour can be reproduced on a multi-core machine by patching the function `GetNumCores()` to return 1 on the master branch and running `feature_nulldummy.py`:

  ```diff
  diff --git a/src/util/system.cpp b/src/util/system.cpp
  index 30d4103..149b512fc 100644
  --- a/src/util/system.cpp
  +++ b/src/util/system.cpp
  @@ -1338,7 +1338,7 @@ bool SetupNetworking()

   int GetNumCores()
   {
  -    return std::thread::hardware_concurrency();
  +    return 1;
   }
  ```
  As solution, parallel script verification is disabled (`-par=1`) and the exact reject reason is checked, which also increases the precision of the test (the possibility that the block is rejected because of another unintended reason is ruled out). See also related PR #22711 which applies the same approach for the p2p segwit test. The PR also includes a refactoring commit which changes the calls to `self.block_submit()` to use named arguments and removes the default value for parameter `accept` (i.e. explicitely passing `accept=...` is mandatory), with the aim to increase the test readability.

ACKs for top commit:
  josibake:
    ACK 7720d4f
  Saviour1001:
    Tested ACK <code>[7720d4f](https://github.com/bitcoin/bitcoin/commit/7720d4f650015272dc7109238230520f71858c6c)</code>

Tree-SHA512: 8a31ebab3e2ab38e555d7a23139b3324a134a0dedc5b879a2419348ae858323882dbbfcbbf88b68e4f8d7eea8cfe43ee19da1d0d2a36c93ae7878c4980cac31d

… p2p_segwit.py

45827fd test: check for block reject reasons in p2p_segwit.py [2/2] (Sebastian Falbesoner)
4eb532f test: check for block reject reasons in p2p_segwit.py [1/2] (Sebastian Falbesoner)
b1488c4 test: fix reference to block processing test in p2p_segwit.py (Sebastian Falbesoner)

Pull request description:

  In the test `p2p_segwit.py`, there are many instances where we send a segwit block to a node with the expectation that it is rejected. For this purpose, the helper function `test_witness_block` exists which allows also to check for a specific reject `reason` that is asserted in the debug log:
  https://github.com/bitcoin/bitcoin/blob/502d22ceed1f90ed41336260f8eb428d3acaf514/test/functional/p2p_segwit.py#L119-L120

  This PR aims to increase the precision of the tests by adding the expected reject reasons to all `test_witness_block` call instances (found via `grep`ing after `test_witness_block(.*accepted=False`). For some blocks that are rejected due to failed script verification, the exact reason is only shown in the debug log if parallel script verification is disabled. For this reason, the addition of the reasons is split up in two commits:
  * first, all instances are tackled that are not subject to script verification, i.e. it doesn't matter whether parallel script verification is enabled or not (e.g. `bad-blk-weight`, `bad-witness-merkle-match`...)
  * then, we explicitely set `-par=1` to only use one script thread, and add the remaining reasons (`non-mandatory-script-verify-flag` with the more specific reason in parantheses)

ACKs for top commit:
  stratospher:
    tested ACK 45827fd.

Tree-SHA512: 00f31867f11d48b38a42b1e79a1303bda1c797ccf3d8c73e6107d70b062604d51ee2a3f2251e7f068dfafdaf09469d27dfee438d9bc9ebaef7febc4b6ef90a95