add CO_ASSERT_THROW to gtest helpers
add CO_ASSERT_THROW to gtest helpers

Summary:
I found many same definitions of this macro in different projects.
I decided to add it to folly library and delete previous duplicate definitions.

Reviewed By: yfeldblum

Differential Revision: D37691220

fbshipit-source-id: c4ab4c99210ebacf27eab4b31714a3d897b8fafe

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly