Retry integration tests when they fail

[jcreedcmu]

Integration tests have been flaky. I tracked down the problem to the vscode electron binary sometimes segfaulting after all tests have been successfully run. The information the test runner gets from vscode-test unfortunately does not distinguish this segfault from test failure. See comments for what we could do about this.

I tried bisecting which integration test, if any, was causing the problem, without much success --- locally I get a segfault rate of about 0.5%-5% depending on which tests are present. It seems like the fewer tests are included in the suite, the fewer segfaults, but artificially duplicating tests doesn't make the segfaults tractably common. A minimal commandline to (possibly) trigger the segfault, after npm run integration has been run at least once, is

$PATH_UP_TO/vscode-codeql/.vscode-test/vscode-1.42.1/VSCode-linux-x64/code  \
  --disable-extensions \
  --extensionDevelopmentPath=$PATH_UP_TO/vscode-codeql/extensions/ql-vscode \
  --extensionTestsPath=$PATH_UP_TO/vscode-codeql//extensions/ql-vscode/out/vscode-tests/no-workspace/index

I wrapped this in a bash while loop waiting for $? to be 139. The .vscode-test/vscode-1.42.1/VSCode-linux-x64/code binary downloaded by vscode-test is stripped of debugging symbols so I wasn't able to get any insight from the coredump.

[aeisenberg]

A very small comment. Looks fine to me, but I don't really have the background on this yet to approve.

[henrymercer]

No docs impact