Merge bitcoin/bitcoin#27941: test: Fix intermittent issue in mining_getblocktemplate_longpoll.py

fa748c6f2ac2f9cac7ce42fd745ed3c3eae093b7 test: Fix intermittent issue in mining_getblocktemplate_longpoll.py (MarcoFalke)

Pull request description:

  Fixes https://github.com/bitcoin/bitcoin/issues/26962

  Wait for the thread to have started and the RPC to have reached the node before continuing. Otherwise the test may run into a race.

  For example:

  ```
   test  2023-06-23T13:10:29.245000Z TestFramework (INFO): Test that introducing a new transaction into the mempool will terminate the longpoll
   node0 2023-06-23T13:10:29.245712Z [http] [httpserver.cpp:254] [http_request_cb] [http] Received a POST request for / from 127.0.0.1:43568
   node0 2023-06-23T13:10:29.245915Z [httpworker.3] [rpc/request.cpp:181] [parse] [rpc] ThreadRPCServer method=getblocktemplate user=__cookie__
   node0 2023-06-23T13:10:29.252594Z [http] [httpserver.cpp:254] [http_request_cb] [http] Received a POST request for / from 127.0.0.1:43568
   node0 2023-06-23T13:10:29.254545Z [httpworker.2] [rpc/request.cpp:181] [parse] [rpc] ThreadRPCServer method=getblockchaininfo user=__cookie__
   node0 2023-06-23T13:10:29.256530Z [http] [httpserver.cpp:254] [http_request_cb] [http] Received a POST request for / from 127.0.0.1:43568
   node0 2023-06-23T13:10:29.256741Z [httpworker.1] [rpc/request.cpp:181] [parse] [rpc] ThreadRPCServer method=sendrawtransaction user=__cookie__
   node0 2023-06-23T13:10:29.258033Z [httpworker.1] [validationinterface.cpp:213] [TransactionAddedToMempool] [validation] Enqueuing TransactionAddedToMempool: txid=38335600f2465c0f8bb2b86d5830a34851d86fa879800c0e1434ddfc78c42898 wtxid=c033cd3efd301c369d66cf759769159609471bd4f9efb3ee30e7209e57b74778
   node0 2023-06-23T13:10:29.258263Z [httpworker.1] [txmempool.cpp:660] [check] [mempool] Checking mempool with 1 transactions and 1 inputs
   node0 2023-06-23T13:10:29.258542Z [scheduler] [validationinterface.cpp:213] [operator()] [validation] TransactionAddedToMempool: txid=38335600f2465c0f8bb2b86d5830a34851d86fa879800c0e1434ddfc78c42898 wtxid=c033cd3efd301c369d66cf759769159609471bd4f9efb3ee30e7209e57b74778
   node0 2023-06-23T13:10:29.259549Z [http] [httpserver.cpp:254] [http_request_cb] [http] Received a POST request for / from 127.0.0.1:43568
   node0 2023-06-23T13:10:29.259745Z [httpworker.0] [rpc/request.cpp:181] [parse] [rpc] ThreadRPCServer method=decoderawtransaction user=__cookie__
   node0 2023-06-23T13:10:29.261066Z [http] [httpserver.cpp:254] [http_request_cb] [http] Received a POST request for / from 127.0.0.1:52690
   node0 2023-06-23T13:10:29.261803Z [http] [httpserver.cpp:254] [http_request_cb] [http] Received a POST request for / from 127.0.0.1:43568
   node0 2023-06-23T13:10:29.262770Z [httpworker.2] [rpc/request.cpp:181] [parse] [rpc] ThreadRPCServer method=getblocktemplate user=__cookie__
  ```

  (`sendrawtransaction` is called before `getblocktemplate`)

ACKs for top commit:
  jamesob:
    Github ACK https://github.com/bitcoin/bitcoin/pull/27941/commits/fa748c6f2ac2f9cac7ce42fd745ed3c3eae093b7
  theStack:
    ACK fa748c6f2ac2f9cac7ce42fd745ed3c3eae093b7

Tree-SHA512: c67d9ec7c56e8a22c1a26a3c3d4d4a4bcc17e4282cad0d66561ba2abd6e92240cb028369b4edc6077ea34e8736c0294f6066381979aee22a6166580cea43729a

0 files changed, 0 insertions, 0 deletions