Merge bitcoin/bitcoin#26651: test: Avoid intermittent timeout in feature_assumevalid.py

fa34e5f3d35c81bb4376337f4f76c3d501bca742 test: Avoid intermittent timeout in feature_assumevalid.py (MarcoFalke)

Pull request description:

  Currently the test will spin up p2p connections in the beginning, then announce the headers to all nodes, but only send the blocks sequentially. This takes a long time, so when getting to the last node, it will have already timed out, while node1 is busy eating blocks. Example:

  ```
   node2 2022-12-06T19:31:35.419291Z [msghand] [net_processing.cpp:5783] [SendMessages] [net] Requesting block 2cfdb317b3b901f79e2d4f96339d0c0dffd8ef2685d324f62ab0e2fa3402430e (1) peer=0
   node2 2022-12-06T19:31:35.424784Z [msghand] [net.cpp:2776] [PushMessage] [net] sending getdata (577 bytes) peer=0
  [...]
   node2 2022-12-06T19:41:35.423257Z [msghand] [net_processing.cpp:5729] [SendMessages] Timeout downloading block 2cfdb317b3b901f79e2d4f96339d0c0dffd8ef2685d324f62ab0e2fa3402430e from peer=0, disconnecting
   node1 2022-12-06T19:41:35.438706Z [msghand] [net_processing.cpp:5783] [SendMessages] [net] Requesting block 6575919043306ed309014d0bd79814b4fab8afaa281e026d8cc3a1c4c2336fbc (1748) peer=0
   node2 2022-12-06T19:41:35.521253Z [net] [net.cpp:573] [CloseSocketDisconnect] [net] disconnecting peer=0
   node2 2022-12-06T19:41:35.630417Z [net] [net_processing.cpp:1532] [FinalizeNode] [net] Cleared nodestate for peer=0
  ```

  Fix this by only spinning up the p2p connection right before they are needed.

ACKs for top commit:
  jamesob:
    ACK fa34e5f3d35c81bb4376337f4f76c3d501bca742 ([`jamesob/ackr/26651.1.MarcoFalke.test_avoid_intermittent`](https://github.com/jamesob/bitcoin/tree/ackr/26651.1.MarcoFalke.test_avoid_intermittent))

Tree-SHA512: 7a1b114c07dfa30237c8cd8637dd6646c5c2dc2530c9de61db231738fddc800b620c31dc664237e33d35e951cf161f015fda593162efc9d85c5f68c6e37217d4

0 files changed, 0 insertions, 0 deletions