refactor SoLoader initialization
refactor SoLoader initialization

Summary: refactor initialization in preparation to change the SoSources locking to use a reader/writer lock

Reviewed By: longinoa

Differential Revision: D6943396

fbshipit-source-id: 7d8ba5b9e3b22fc4ea92f0b63fc0c5c6a98ea879

facebook/SoLoader,facebook/SoLoader,facebook/SoLoader