SSS_CLIENT: got rid of using PRNG
    
    1) no reason to expect "thundering herd issue"
    2) randomization as it was done (strictly 1 or 2 secs)
       would not help much anyway
    3) usage of PRNG might break app that depends on deterministic
       PRNG behaviour
    
    Resolves: https://pagure.io/SSSD/sssd/issue/4094
    
    Reviewed-by: Michal Židek <mzidek@redhat.com>