folder_branch_ops: combine retries with runUnlessCanceled
folder_branch_ops: combine retries with runUnlessCanceled

Suggested by @akalin-keybase.

Issue: #632

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