Add a method to load vendor_service_context only.

This is used by vndservicemanager, which will only
have access to the vndservice_contexts on the vendor
partition.

Bug: 36052864
Test: vndservicemanager can load the context

(cherry-pick from commit 69e45cdfeed073fd0fcf648444b1e606ee739949)

Change-Id: I26ebf40906d6c56a3cfa4a20b731e101614fe6e6
Merged-In: Ifd5caa4f74236184ef970ce39a8be227c50b48d4
3 files changed