Fix feature_dbcrash failure

Summary:
feature_dbcrash.py keeps failing on my machine due to the
wait_for_node_exit timeout being too short. I cannot reproduce on
other machines, maybe this is due the WSL being very slow on disk IO ?
Increasing the timeout fixes the issue.

Test Plan:

./test/functional/test_runner.py feature_dbcrash

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2566