sudo: fetch sudoRunAs attribute
    
    This attribute was used in pre 1.7 versions of sudo and it is now
    deprecated by sudoRunAsUser and sudoRunAsGroup. However, some users
    still use this attribute so we need to support it to ensure backward
    compatibility.
    
    This patch makes sure that this attribute is downloaded if present and
    provided to sudo. Sudo than decides how to handle it.
    
    The new mapping option is not present in a man page since this
    attribute is deprecated in sudo for a very long time.
    
    Resolves:
    https://fedorahosted.org/sssd/ticket/2212
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>
    (cherry picked from commit 7c30e60c525ea798aaab142766ff00eef4b5df3b)