Summary:
- Capitalise productFlavorName for target path
- Capitalise buildType in sourceName when flavour exists
- Fix the path the assets are added.
- Backward compatibility with bundleIn(buildTypeName) when flavours are added
Closes https://github.com/facebook/react-native/pull/5580
Reviewed By: svcscm
Differential Revision: D2911735
Pulled By: mkonicek
fb-gh-sync-id: 6fb391a12ee27ee2a503961d8779a85d31cf5367