[infra-tests] Stop the stability checker running on multiple commits on master. (#5196)

The stability checker tried to work out which commits to test by
looking at all the commits on the current branch that aren't on
another branch. But if the current branch is e.g. master then this
will produce many more commits than intended. To fix this use the
merge-base with master when it's closer to HEAD than the last commit
not on another branch.

View on GitHub: https://github.com/w3c/web-platform-tests/pull/5196

Received on Wednesday, 22 March 2017 12:22:52 UTC