redirector: handle mountpoints like  /Volumes/Keybase (user)
redirector: handle mountpoints like  /Volumes/Keybase (user)

Issue: KBFS-2820

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