Merge #19804: test/refactor: reference p2p objects explicitly and remove confusing Test_Node.p2p property

10d61505fe [test] remove confusing p2p property (gzhao408)
549d30faf0 scripted-diff: replace p2p with p2ps[0] in p2p_invalid_tx (gzhao408)
7a0de46aea [doc] sample code for test framework p2p objects (gzhao408)
784f757994 [refactor] clarify tests by referencing p2p objects directly (gzhao408)

Pull request description:

  The `TestNode` has a `p2p` property which is an alias for `p2ps[0]`.

  I think this should be removed because it can be confusing and misleading (to both the test writer and reviewer), especially if a TestNode has multiple p2ps connected (which is the case for many tests).
  Another example is when a test has multiple subtests that connect 1 p2p and use the `p2p` property to reference it. If the subtests don't completely clean up after themselves, the subtests may affect one another.

  The best way to refer to a connected p2p is use the object returned by `add_p2p_connection` like this:
  ```py
  p2p_conn = node.add_p2p_connection(P2PInterface())
  ```
  A good example is [p2p_invalid_locator.py](https://github.com/bitcoin/bitcoin/blob/master/test/functional/p2p_invalid_locator.py), which cleans up after itself (waits in both `wait_for_disconnect` and in `disconnect_p2ps`) but wouldn't need so much complexity if it just referenced the connections directly.

  If there is only one connected, it's not really that tedious to just use `node.p2ps[0]` instead of `node.p2p` (and it can always be aliased inside the test itself).

ACKs for top commit:
  robot-dreams:
    utACK 10d61505fe
  jnewbery:
    utACK 10d61505fe
  guggero:
    Concept ACK 10d61505.

Tree-SHA512: 5965548929794ec660dae03467640cb2156d7d826cefd26d3a126472cbc2494b855c1d26bbb7b412281fbdc92b9798b9765a85c27bc1a97f7798f27f64db6f13

test/functional/p2p_blocksonly.py

@@ -17,7 +17,7 @@ class P2PBlocksOnly(BitcoinTestFramework):
         self.extra_args = [["-blocksonly"]]
 
     def run_test(self):
-        self.nodes[0].add_p2p_connection(P2PInterface())
+        block_relay_peer = self.nodes[0].add_p2p_connection(P2PInterface())
 
         self.log.info('Check that txs from p2p are rejected and result in disconnect')
         prevtx = self.nodes[0].getblock(self.nodes[0].getblockhash(1), 2)['tx'][0]
@@ -41,20 +41,20 @@ class P2PBlocksOnly(BitcoinTestFramework):
         )['hex']
         assert_equal(self.nodes[0].getnetworkinfo()['localrelay'], False)
         with self.nodes[0].assert_debug_log(['transaction sent in violation of protocol peer=0']):
-            self.nodes[0].p2p.send_message(msg_tx(FromHex(CTransaction(), sigtx)))
-            self.nodes[0].p2p.wait_for_disconnect()
+            block_relay_peer.send_message(msg_tx(FromHex(CTransaction(), sigtx)))
+            block_relay_peer.wait_for_disconnect()
             assert_equal(self.nodes[0].getmempoolinfo()['size'], 0)
 
         # Remove the disconnected peer and add a new one.
         del self.nodes[0].p2ps[0]
-        self.nodes[0].add_p2p_connection(P2PInterface())
+        tx_relay_peer = self.nodes[0].add_p2p_connection(P2PInterface())
 
         self.log.info('Check that txs from rpc are not rejected and relayed to other peers')
         assert_equal(self.nodes[0].getpeerinfo()[0]['relaytxes'], True)
         txid = self.nodes[0].testmempoolaccept([sigtx])[0]['txid']
         with self.nodes[0].assert_debug_log(['received getdata for: wtx {} peer=1'.format(txid)]):
             self.nodes[0].sendrawtransaction(sigtx)
-            self.nodes[0].p2p.wait_for_tx(txid)
+            tx_relay_peer.wait_for_tx(txid)
             assert_equal(self.nodes[0].getmempoolinfo()['size'], 1)
 
         self.log.info('Check that txs from peers with relay-permission are not rejected and relayed to others')