va: compute maxRemoteFailures based on MPIC

[jsha]

Previously this was a configuration field.

Ports maxAllowedFailures() from determineMaxAllowedFailures() in #7794.

Test updates:

Remove the maxRemoteFailures param from setup in all VA tests.

Some tests were depending on setting this param directly to provoke failures.

For example, TestMultiVAEarlyReturn previously relied on "zero allowed failures". Since the number of allowed failures is now 1 for the number of remote VAs we were testing (2), the VA wasn't returning early with an error; it was succeeding! To fix that, make sure there are two failures. Since two failures from two RVAs wouldn't exercise the right situation, add a third RVA, so we get two failures from three RVAs.

Similarly, TestMultiCAARechecking had several test cases that omitted this field, effectively setting it to zero allowed failures. I updated the "1 RVA failure" test case to expect overall success and added a "2 RVA failures" test case to expect overall failure (we previously expected overall failure from a single RVA failing).

In TestMultiVA I had to change a test for len(lines) != 1 to len(lines) == 0, because with more backends we were now logging more errors, and finding e.g. len(lines) to be 2.

[github-actions]

@jsha, this PR appears to contain configuration and/or SQL schema changes. Please ensure that a corresponding deployment ticket has been filed with the new values.

[beautifulentropy]

You've got a CI failure:

--- FAIL: TestMultiVALogging (0.00s)
    va_test.go:636: expected perspective of VA to be dev-arin

[jsha]

Test failure is a race condition fixed in #7811.

[jsha]

The tests are now fixed.

[jsha]

Main merged, conflicts resolved, tests passing again 🎉