roachtest: use structured errors

[smg260]

roachtest predates cockroachdb/errors and as a result so far hasn't
capitalized many improvements. Today, roachtest errors are often noisy.

This commit adopts cockroachdb/errors and reaps some of the immediate
rewards, while making related improvements that would also have been
possible without the adoption.

The main user-facing change is that error messages in the output are now
a lot more concise; these would previously - sometimes - include the
entire stack trace. Now they contain only the topmost stack record of
the innermost error:

(test_test.go:129).func3: first error
(test_test.go:130).func3: second error

The full error continues to be logged, but we write it to files in
the artifacts, where they can be inspected just in case. This now
happens unconditionally for all errors, whereas the old code only
logged the stacks if the error was reported in a certain way.

Internally, the reorganization has also considerably simplified
roachtest. Stack frame offset tracking has been removed, since
cockroachdb/errors already handles it. Custom rendering code
was similarly significantly trimmed down.

In making this change, I opted to always have roachtest create
loggers backed by real files. This was previously elided in tests,
but this would have caused extra conditionals. It's better to
standardize on the way in which roachtest is always used in
actual invocations.

Looking ahead, structured errors open a few avenues:

• can assign the owner based on the type of failure. For example,
  roachtest: opt some tests into aggressive stats checks #87106 wants consistency check failures to always go to the KV
  team, regardless of which test's cluster was being checked.

  Failures during an IMPORT/RESTORE (common across all tests) could be
  routed to the Disaster Recovery team by default (assuming we provide a
  wrapper around these operations that all tests use and which does this
  wrapping).

• Similarly, SSH failures can be special cased via a marking error
  and can be directed away from the owning team, which can't do
  anything about them anyway (roachtest: special-case SSH_PROBLEM as infra flakes #82398).

• We can conceivably start grouping failure modes by "error signature".
  That is, errors which have a "comparable" chain of errors (e.g. same
  types, and within formatted errors the same format string). Issues
  could then be reused only for compatible error signatures.

Release note: NoneBackport:

• 1/1 commits from "roachtest: use structured errors" (roachtest: use structured errors #88556)
• 3/3 commits from "Roachtest redirect SSH flakes to test-eng" (Roachtest redirect SSH flakes to test-eng #88492)
• 1/1 commits from "Revert fmtsafe.go output" (Revert fmtsafe.go output #90720)
• 1/1 commits from "Roachtest SSH Retries" (Roachtest SSH Retries #90451)
• 1/1 commits from "roachtest: Retry failed SCP attempts in the same way as SSH commands." (roachtest: Retry failed SCP attempts in the same way as SSH commands. #92082)

Please see individual PRs for details.

/cc @cockroachdb/release

[cockroach-teamcity]

This change is 

[srosenberg]

Thanks for rebasing!