Widen scope of --ignore-module

[Al33t]

With the release of v0.14 it is no longer possible to skip rules which import the vt module as it is now a known module whereas --ignore-module only skips modules that are otherwise flagged as unsupported. This poses an issue since the vt module only implements a subset so vt.metadata and vt.behaviour are flagged as errors. Would it not make sense to be able to selectively be able to unconditionally ignore these errors as they're now somewhat of a regression?

[Al33t]

This would be a bit more restrictive version of #244.