Feature request: ignore_failures heuristic should be able to be overridden on the command line

[kevemueller]

Brew test-bot uses complex heuristics to determine whether to set ignore_failures.
ignore_failures is set based on the state of the current formula, whether it is bottled, bottled on current version, etc.

These heuristics perform bad if the default strategy of the tap is not to bottle everything.
A command-line switch --never-ignore-failures would help to always falsify ignore_failures and hence allow unbottled formulae still to fail when tested.

This is similar to #1178, but not the same.

[MikeMcQuaid]

Will review a PR on this but brew test-bot (and Homebrew itself) are primarily designed for workflows where bottling everything is the intent.