…t exists

fa90a89 [test] combine_logs: append node stderr and stdout if it exists (MarcoFalke)

Pull request description:

  See issue:

  * tests: bitcoind stdout and error should be passed to the logger #13519

ACKs for commit fa90a8:
  laanwj:
    utACK fa90a89

Tree-SHA512: 39c4596e2e133c9011ab01bc4dc24e884d0a8cce7a67d3765f17c288d3ffbd438e1ff6016d0f817a981b27fce17fa77a1ff56787ddb1ea55123ce9ecffb44c08

…ut if it exists

fa90a89 [test] combine_logs: append node stderr and stdout if it exists (MarcoFalke)

Pull request description:

  See issue:

  * tests: bitcoind stdout and error should be passed to the logger bitcoin#13519

ACKs for commit fa90a8:
  laanwj:
    utACK fa90a89

Tree-SHA512: 39c4596e2e133c9011ab01bc4dc24e884d0a8cce7a67d3765f17c288d3ffbd438e1ff6016d0f817a981b27fce17fa77a1ff56787ddb1ea55123ce9ecffb44c08

Summary:
Description of issue that motivated this PR:

>Currently the stdout of bitcoinds in functional tests is written to a file in self.datadir of the node. It is only read/examined after the node is shut down. To aid debugging it should (also?) be passed to the logger for visibility and timestamps.

Backport of Core [[bitcoin/bitcoin#15841 | PR15841]]
Depends on D7795

Test Plan:
Intentionaly modify a functional test to make it fail, then check that node stdout is now part of the combined logs.
```
ninja
../test/functional/feature_bip68_sequence.py --configfile=./test/config.ini
../test/functional/combine_logs.py -c
```

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D7796

…ut if it exists

fa90a89 [test] combine_logs: append node stderr and stdout if it exists (MarcoFalke)

Pull request description:

  See issue:

  * tests: bitcoind stdout and error should be passed to the logger bitcoin#13519

ACKs for commit fa90a8:
  laanwj:
    utACK fa90a89

Tree-SHA512: 39c4596e2e133c9011ab01bc4dc24e884d0a8cce7a67d3765f17c288d3ffbd438e1ff6016d0f817a981b27fce17fa77a1ff56787ddb1ea55123ce9ecffb44c08

Merge bitcoin PRs: bitcoin#14683, bitcoin#15841, bitcoin#14984 and bitcoin#15943

…ut if it exists

fa90a89 [test] combine_logs: append node stderr and stdout if it exists (MarcoFalke)

Pull request description:

  See issue:

  * tests: bitcoind stdout and error should be passed to the logger bitcoin#13519

ACKs for commit fa90a8:
  laanwj:
    utACK fa90a89

Tree-SHA512: 39c4596e2e133c9011ab01bc4dc24e884d0a8cce7a67d3765f17c288d3ffbd438e1ff6016d0f817a981b27fce17fa77a1ff56787ddb1ea55123ce9ecffb44c08