Fix create command to properly handle keyfile size.

Fix create command to properly handle keyfile size.

- for keyfile reset hash, it make no sense (see man page)
- use activate_by_keyfile to make code more readable
(it still does the stem thing)

- if keyfile specified, read only key and do not do exhausted
read (regression from 1.1.3)

git-svn-id: https://cryptsetup.googlecode.com/svn/trunk@399 36d66b0a-2a48-0410-832c-cd162a569da5