Update user passwords in keystone_register provider

When trying to create a user, if the user already exists, we were not
doing anything so far.

However, if the password is different, we need to udpate it. To avoid
changing the password with no reason, we try to get a token with the
password, and if it doesn't work, we update the password.

https://bugzilla.novell.com/show_bug.cgi?id=825622
Fix log messages

One message was talking about user instead of role, and the punctuation
wasn't totally right.
Delete the tokens that we create to test the password
Merge pull request #82 from vuntz/update-passwords

Update user passwords in keystone_register provider