fix(test): Show full Zebra test panic details in CI logs

[teor2345]

Motivation

We're seeing some Zebra panics in CI. Our custom test harness just reports "The application panicked (crashed).", with no details.

Example logs:
https://github.com/ZcashFoundation/zebra/runs/7981879420?check_suite_focus=true#step:6:1103

Depends-On: #4945

Solution

• Add output logs to test context, and add test harness tests to check it works
• Let empty test child logs be read again (and produce empty output

Related refactors:

• Add an ignore_exited argument to test child process kill()
• Handle test failure regexes using Result::Err, rather than panicking

Related changes:

• Log the command timeout when an acceptance test fails

Review

This is an urgent fix, so we can see panic details in our CI logs.

Reviewer Checklist

• CI passes

[codecov]

Codecov Report

Merging #4942 (1f72f3a) into main (1d861b0) will increase coverage by 0.06%.
The diff coverage is 76.69%.

@@            Coverage Diff             @@
##             main    #4942      +/-   ##
==========================================
+ Coverage   79.04%   79.11%   +0.06%     
==========================================
  Files         309      309              
  Lines       38781    38830      +49     
==========================================
+ Hits        30656    30720      +64     
+ Misses       8125     8110      -15     

[teor2345]

Now we know what the panic bug is, this isn't a critical priority any more.

[teor2345]

Marking this as critical because we're still seeing panics, and we need to know what they are. So we want to merge this first.

[teor2345]

@Mergifyio update

[mergify]

update

✅ Branch has been successfully updated

[teor2345]

I added some extra test debug output in commit 9d4c709. Alfredo and I talked about it earlier this week to make it easier to diagnose test failures.

I was going to put it in PR #4958, but that might have conflicted with this PR, so I put it here instead.

[teor2345]

@Mergifyio update

[mergify]

update

✅ Branch has been successfully updated

[gustavovalverde]

Approving as this is critical and CI is passing.