Filter packages based on the working directory

[bonsairobo]

For example, if we run tests with -w foo we should only run the tests inside of foo.

I'm not sure what the best mechanism is yet. We could either do this filtering during construction of CrateGraph or after. But I worry that it might somehow interact with the dependency graph resolution and create a subtle bug. This requires care.

[loispostula]

We already have the whitelist for this, I fixed it for publish and tests in #269

We still need to implement it for fix-lock-files

[bonsairobo]

The whitelist would require that you manually enumerate all packages in a directory and pass them to --whitelist. I'm proposing the tool should be able to do this automatically.

[loispostula]

Yeah, it's probably a bug