Make test runner more flexible for running fast tests.

Make test runner more flexible for running fast tests.

Transformed variant flags into named variants. Now, all combinations of variants can be specified on the command line. The old command-line flags are kept for backwards compatibility on the bots.

Added two new test groups: slow and pass|fail. Both are implemented similar to the flaky test feature and allow to either skip or run tests marked as slow or as pass|fail.

R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/85733003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@18062 ce2b1a6d-e550-0410-aec6-3dcde31c8c00