Store password in vold

If we are not to double prompt, we need to pass the password from
CryptKeeper to KeyStore. Since the entire framework is taken down
and restarted, we must store the password in a secure system daemon.
There seems no better way than holding it in vold.

Change-Id: Ia60f2f051fc3f87c4b6468465f17b655f43f97de
3 files changed