folder_branch_ops: check last flush error when waiting for journal
folder_branch_ops: check last flush error when waiting for journal

Issue: KBFS-1609

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