auth: Increase delay before background tasks start
auth: Increase delay before background tasks start

I've observed failures due to "missing" the peer nodes by about 1
second. Adding 5 second to the existing delay should cover most false
negative test results.

Fixes #3320.

scylladb/scylla,avikivity/scylla,duarten/scylla,duarten/scylla,duarten/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla