Adding yaml-cpp fboss code for oss

Summary: Added yaml-cpp library to the fboss OSS build

Reviewed By: shri-khare

Differential Revision: D25126509

fbshipit-source-id: 1e88150dbf8c96a5ac696e003265dc1f14bec105

Author: Rajan Kumar

build/fbcode_builder/manifests/fboss

@@ -32,6 +32,7 @@ libsai
 OpenNSA
 re2
 python
+yaml-cpp
 
 [shipit.pathmap]
 fbcode/fboss/github = .