Allow runlint to work with multiple eslintrc files
Allow runlint to work with multiple eslintrc files

Summary:
In D34142, I added a custom .eslintrc to webapp to allow for linting
graphql queries. This caused errors on jenkins when running lint over
the entire codebase, since submodules of webapp may have different
eslint configurations and `runlint.py` was not set up to handle that
situation.

This patch fixes that issue, which should allow for webapp to have its
own .eslintrc file.

Test Plan:
From webapp, I ran:

`ka-lint intl/`

which includes files both from webapp and from subrepos.

Before this patch, this command would fail with an Exception. After this
patch, it succeeds.

I also run `ka-lint` against a list of js and python files chosen at
random within webapp. Using the verbose flag on ka-lint, I verified that
eslint was only called once, unless a js file from a subrepo was
included (in which case it was called twice.)

Reviewers: jared, csilvers

Reviewed By: csilvers

Subscribers: kevinb, john

Differential Revision: https://phabricator.khanacademy.org/D34195

Khan/khan-linter,Khan/khan-linter,Khan/khan-linter,Khan/khan-linter