Merge #16277: [Tests] Suppress output in test_bitcoin for expected errors

7a0c2242890549b6dddac4cc6f1840a528469f2a Suppress output in test_bitcoin for expected errors (Gert-Jaap Glasbergen)

Pull request description:

  Closes #15944

  This adds two methods to noui, that allows temporarily suppressing (and then resuming) the output from `noui`. For situations where errors are expected, it's confusing for the test binary to output an error and then conclude with `No errors detected`.

  It also uses this supress/reconnect in the tests that currently produce verbose errors when running `test_bitcoin`.

  Output of `test_bitcoin` on current master:
  ```
  gertjaap@gjdesktop:~/src/bitcoin$ src/test/test_bitcoin
  Running 351 test cases...
  Error: Specified -walletdir "/tmp/test_common_Bitcoin Core/1561389554_943311758/tempdir/path_does_not_exist" does not exist
  Error: Specified -walletdir "/tmp/test_common_Bitcoin Core/1561389554_643733972/tempdir/not_a_directory.dat" is not a directory
  Error: Specified -walletdir "wallets" is a relative path

  *** No errors detected
  ```

  Output after this code is merged:

  ```
  gertjaap@gjdesktop:~/src/bitcoin$ src/test/test_bitcoin
  Running 351 test cases...

  *** No errors detected
  ```

ACKs for top commit:
  l2a5b1:
    ACK 7a0c224 - tested and reviewed.
  laanwj:
    ACK 7a0c2242890549b6dddac4cc6f1840a528469f2a

Tree-SHA512: c7881f7a431a065329360ffa9937ce4742694c646c90c019d3aff95dfd7fccbdcda9116c5762feb6dfd1108d14f9fb386e203b173c4bde9093afb2b8c977d13d

0 files changed, 0 insertions, 0 deletions