nss: allow UPNs in SSS_NSS_GETSIDBYNAME and SSS_NSS_GETORIGBYNAME
    
    When adding support for UPNs, email addresses and aliases the
    SSS_NSS_GETSIDBYNAME and SSS_NSS_GETORIGBYNAME request were forgotten.
    This patch adds the missing support because it might be irritating if
    getpwnam() can resolve the name but the other requests fail. The same
    logic as for the plain user lookup is used, this add some code
    duplication which is expected to be removed when the nss responder will
    be switched to use the new cache_req code.
    
    Resolves https://fedorahosted.org/sssd/ticket/3194
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>