test: make sure user's configuration or environment does not affect tests

[stamblerre]

Some tests in the extension fail when the user running them has unexpected configurations or when they don't have the correct tools installed. We should make sure all test runs are independent of the user's environment.

microsoft/vscode-go#801 describes a specific fix that should be applied to one of the tests.

[hyangah]

That's one of the motivation I had when adding the docker-based setup build/all.bash.

Another approach is to utilize --user-data-dir e.g.,
https://github.com/golang/vscode-go/blob/master/.vscode/launch.json#L66

(reference: https://vscode-dev-community.slack.com/archives/C74CB59NE/p1585956905048000)

[hyangah]

Seems like the --user-data-dir trick no longer works. Filed microsoft/vscode#97995

[gopherbot]

Change https://golang.org/cl/238001 mentions this issue: test: increase timeout and skip gopls update check in testing

[gopherbot]

Change https://golang.org/cl/267217 mentions this issue: test/goDebugConfiguration.test.ts: test settings.json debug config effects

[hyangah]

The adjustment made by https://go-review.googlesource.com/c/vscode-go/+/267217 fixed this issue. Thanks @suzmue !