Refactored binary_util methods to be wrapped inside BinaryUtil object.

BinaryUtil can be initialized with bootstrap_dir, baseurls, and timeout; missing parameters are loaded from config.
See John's comment on https://rbcommons.com/s/twitter/r/556 .

Testing Done:
Existing test cases didn't break.

Reviewed at https://rbcommons.com/s/twitter/r/605/