Download symbol file for .oat files on android

On android .oat files (compiled java code) don't have symbol
information but on SDK 23+ it can be generated by the oatdump tool
(based on the dex information).

This CL adds logic to download this information and store it in the
module cache.

Differential revision: http://reviews.llvm.org/D11936

llvm-svn: 244738