Use loginname instead of display name

getDisplayName would return the display name of the user, not great if it is a
canonical string. The uid passed back from 'login' is the UUID of the user, so
also not suitable. The login name from the session is the username the user
used to log in to ownCloud in the first place, which is what is needed.
Revoke sharable permission on automatic SMB shares

Shares authenticated with user credentials (aka not hard coded) cannot be
accessed by other users, breaking sharing. This change completely revokes
sharing for such shares