Skylarkify ReactNative OSS build defs.
Skylarkify ReactNative OSS build defs.

Summary:
Skylark parser will not allow access to file system other
than through `glob` and environment variables. The logic was also
making assumption about `buck-out` layout structure which is not
specified and as such is subject to change at any time without any
announcement.

Differential Revision: D8604721

fbshipit-source-id: 90826b4d5709580aad3092d0331d0e84e493c3b8

hammerandchisel/react-native,facebook/react-native,javache/react-native,exponentjs/react-native,janicduplessis/react-native,janicduplessis/react-native,facebook/react-native,exponentjs/react-native,javache/react-native,hammerandchisel/react-native,hoangpham95/react-native,exponent/react-native,exponent/react-native,pandiaraj44/react-native,javache/react-native,facebook/react-native,javache/react-native,javache/react-native,myntra/react-native,exponent/react-native,facebook/react-native,myntra/react-native,arthuralee/react-native,hammerandchisel/react-native,exponent/react-native,facebook/react-native,hoangpham95/react-native,hammerandchisel/react-native,janicduplessis/react-native,pandiaraj44/react-native,pandiaraj44/react-native,janicduplessis/react-native,arthuralee/react-native,exponentjs/react-native,exponentjs/react-native,myntra/react-native,exponent/react-native,hoangpham95/react-native,javache/react-native,hoangpham95/react-native,hoangpham95/react-native,javache/react-native,exponentjs/react-native,facebook/react-native,myntra/react-native,myntra/react-native,hammerandchisel/react-native,exponentjs/react-native,myntra/react-native,arthuralee/react-native,facebook/react-native,exponentjs/react-native,exponent/react-native,janicduplessis/react-native,exponentjs/react-native,javache/react-native,pandiaraj44/react-native,hammerandchisel/react-native,hoangpham95/react-native,myntra/react-native,janicduplessis/react-native,hoangpham95/react-native,arthuralee/react-native,janicduplessis/react-native,arthuralee/react-native,facebook/react-native,facebook/react-native,exponent/react-native,janicduplessis/react-native,hammerandchisel/react-native,pandiaraj44/react-native,myntra/react-native,pandiaraj44/react-native,hoangpham95/react-native,exponent/react-native,hammerandchisel/react-native,javache/react-native,pandiaraj44/react-native,myntra/react-native,pandiaraj44/react-native