PROXY: Use the fqname when converting to lowercase
    
    When saving the user there is a comparison between the "cased alias"
    and the "lowercase password name". However, the first doesn't use fully
    qualified name while the second does, resulting in a not expected
    override of the "nameAlias" attribute of a stored user when trying to
    authenticate more than once using an alias.
    
    Resolves:
    https://fedorahosted.org/sssd/ticket/3134
    
    Signed-off-by: Fabiano Fidêncio <fidencio@redhat.com>
    Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>