Merge #19429: test: Fix intermittent failure in wallet_encryption

fabd33b5416f2a2cd635d02b85d5bc2681cfaf17 test: Fix intermittent failure in wallet_encryption (MarcoFalke)

Pull request description:

  Iterating all crypted keys might take time.

  E.g.

  ```
   node0 2020-07-01T14:41:19.227367Z [httpworker.0] ThreadRPCServer method=walletpassphrase user=__cookie__
   node0 2020-07-01T14:41:24.377142Z [httpworker.0] queue run of timer lockwallet() in 100000000 seconds (using HTTP)
  ...
   test  2020-07-01T14:41:24.379000Z TestFramework (ERROR): Assertion failed
                                     Traceback (most recent call last):
                                       File "/tmp/cirrus-ci-build/ci/scratch/build/bitcoin-x86_64-pc-linux-gnu/test/functional/test_framework/test_framework.py", line 117, in main
                                         self.run_test()
                                       File "/tmp/cirrus-ci-build/ci/scratch/build/bitcoin-x86_64-pc-linux-gnu/test/functional/wallet_encryption.py", line 88, in run_test
                                         assert_greater_than(expected_time + 5, actual_time) # 5 second buffer
                                       File "/tmp/cirrus-ci-build/ci/scratch/build/bitcoin-x86_64-pc-linux-gnu/test/functional/test_framework/util.py", line 54, in assert_greater_than
                                         raise AssertionError("%s <= %s" % (str(thing1), str(thing2)))
                                     AssertionError: 1693614483 <= 1693614484
  ```

  https://cirrus-ci.com/task/5322429885054976?command=ci#L4517

ACKs for top commit:
  achow101:
    ACK fabd33b5416f2a2cd635d02b85d5bc2681cfaf17

Tree-SHA512: 7a3ccdfc0cdc05fef1f942d3167d100ed63422eb54c05405c884ed91162b7bdb5ce54cb5a981b99a6df2e4af1ea834ccd7d5156531c8c14ea13e735becd6b377

0 files changed, 0 insertions, 0 deletions