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>