Ensure race between rollback and roll forward is properly handled

If rollback for a package is committed at the same time the package is
updated, it's possible we will incorrectly roll back the newly updated
version of the application.

Add a hidden API to the package installer that lets you set a required
existing version of a package to be updated. If the expected package
version is not installed at the time of commit, the update install
fails.

The RollbackManager uses this new API to ensure that rollback will fail
if the package in question was just updated.

Test: atest RollbackTest, with new test added and manual confirmation
      that the race condition was exercised by the new test.
Bug: 128831080

Change-Id: Ifa5627e257d2ef13e2b213ef0dbc93932797ce0d