x/build: report failures fast but still make all test results available

[dmitshur]

(This feature request/enhancement is related to issue #34119, the goal is to improve developer experience at the expense of using more computational resources.)

In #14305 (comment), there is discussion of whether to use -k on which branches, and on post-submit only vs trybots too. There is a trade-off in that the flag improves information that a failed build reports, but makes the test failure get reported more slowly.

A more ideal (for user developer experience) solution is to report a failure fast, as soon as the first test fails, but keep going and make all test results available for later viewing by interested parties.

See the fast-finish builds feature of Travis CI for some related precedent.

/cc @bradfitz @bcmills @toothrot @cagedmantis

[gopherbot]

Change https://golang.org/cl/211678 mentions this issue: cmd/coordinator: use 'go tool dist test -k' on release branches

[dmitshur]

/cc @findleyr

[gopherbot]

Change https://golang.org/cl/223780 mentions this issue: [release-branch.go1.13] cmd/doc: skip failing TestDotSlashLookup on Windows

[gopherbot]

Change https://golang.org/cl/223782 mentions this issue: [release-branch.go1.13] cmd/go: fix and skip known Windows test failures