Unify usage of function gethostname
    
    man gethostanme says:
    NOTES
       SUSv2  guarantees  that  "Host  names  are  limited  to   255   bytes".
       POSIX.1-2001 guarantees that "Host names (not including the terminating
       null  byte)  are  limited   to   HOST_NAME_MAX   bytes".    On   Linux,
       HOST_NAME_MAX  is  defined  with the value 64, which has been the limit
       since Linux 1.0 (earlier kernels imposed a limit of 8 bytes).
    
    Reviewed-by: Pavel Březina <pbrezina@redhat.com>
    (cherry picked from commit bf6f1b3d49e17b1adf0448c0b06e94b1e52ddffd)