libfs: fix lock expiration test by giving it something to flush
libfs: fix lock expiration test by giving it something to flush

Issue: KBFS-2477

keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/kbfs,keybase/client,keybase/client