It should be enough to specify --variants=... with the
desired set of variants. The stress/nostress shortcuts
might get confusing soon, as we intend to move the stress
option out of the developer default set.

BUG=v8:5238

Review-Url: https://codereview.chromium.org/2195373002
Cr-Commit-Position: refs/heads/master@{#38248}