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