sss_autofs: Check return value of autofs make request
    
    The return value of function sss_autofs_make_request was not checked.
        (returned value was SSS_STATUS_UNAVAIL)
    Unfotunatelly, errnop was zero; buffer "repbuf" was not initialised
    and automount crashed in sss_autofs plugin.
    
    Resolves:
    https://fedorahosted.org/sssd/ticket/2288
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>
    (cherry picked from commit 71bcdde36bcfd8cb797777062208a85bf6337dec)