Change cryptfs changepw to only require a new password.

The master key is now stored unhashed in memory. This
is needed because certain operation like remote reseting
of passwords the old password is not avaliable.
The changepw interface has been changed to only take
the new password as the only argument. When this is
called we reencrypt the master key with the new password
and old salt.

Bug: 3382129
Change-Id: I9a596b89013194605d6d7790067691aa0dc75e72
diff --git a/cryptfs.h b/cryptfs.h
index 432450c..ca3cc95 100644
--- a/cryptfs.h
+++ b/cryptfs.h
@@ -62,7 +62,7 @@
   int cryptfs_check_passwd(char *pw);
   int cryptfs_restart(void);
   int cryptfs_enable(char *flag, char *passwd);
-  int cryptfs_changepw(char *oldpw, char *newpw);
+  int cryptfs_changepw(char *newpw);
 #ifdef __cplusplus
 }
 #endif