Fix broken test

Previously, flag INSTALL_ALL_USERS  would treat this as an update,
and only do it for the users who already have the app installed.
Since the behavior changes, revise the test accordingly.

Fix: 226813445
Test: atest FrameworksServicesTests:PackageManagerServiceTest#\
        testInstallReason_userRemainsUninstalled_keepUnknown
Change-Id: If9a84c401224dad238485d6728efe3eb7cad02e2