Disable FBOSS OSS tests in on-diff jobs (#183)

Summary:
X-link: facebookincubator/katran#183

X-link: facebook/openr#143

X-link: facebook/fbthrift#536

X-link: facebook/fb303#33

X-link: facebook/folly#1924

FBOSS OSS on-diff job is failing due to random test failures.

Disabling the tests for now to avoid build breakages.

Reviewed By: shri-khare

Differential Revision: D42550176

fbshipit-source-id: fb887cd092adae0a57f7a377fa7e1941c46c5afd

build/fbcode_builder/manifests/fboss

@@ -45,3 +45,6 @@ nlohmann-json
 fbcode/fboss/github = .
 fbcode/fboss/common = common
 fbcode/fboss = fboss
+
+[sandcastle]
+run_tests = off