Disable FBOSS OSS tests in on-diff jobs (facebookincubator#124)

Summary:
X-link: facebook/fboss#124

X-link: facebookincubator/reindeer#6

X-link: facebook/sapling#497

X-link: facebook/mvfst#284

X-link: facebook/wangle#212

X-link: facebookincubator/velox#3785

X-link: facebookexperimental/rust-shed#37

X-link: facebook/hhvm#9317

X-link: facebookexperimental/edencommon#6

Pull Request resolved: facebookincubator#108

X-link: facebook/proxygen#436

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: a40a4d39c2176e4a201f6c49c6e7837c4c7c90e5

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