Wait longer for rndc reconfig effects to complete

The following discussion from !7491 (merged) should be addressed:

• @marka started a discussion: (+1 comment)

  Looks like a timing issue

  I:mkeys:check 'rndc-managed-keys destroy' (28)
  I:mkeys:ns2 destroying managed-keys database for '_default'
  I:mkeys:failed

  06-Feb-2023 23:53:12.342 received control channel command 'managed-keys status'
  06-Feb-2023 23:53:12.434 received control channel command 'managed-keys destroy'
  06-Feb-2023 23:53:12.478 received control channel command 'managed-keys status'
  06-Feb-2023 23:53:12.522 received control channel command 'reconfig .'
  06-Feb-2023 23:53:12.582 scheduled loading new zones
  06-Feb-2023 23:53:12.750 received control channel command 'managed-keys status'
  06-Feb-2023 23:53:12.790 zone_maintenance: managed-keys-zone: enter
  06-Feb-2023 23:53:12.798 dns_zone_maintenance: managed-keys-zone: enter
  06-Feb-2023 23:53:12.806 received control channel command 'secroots -'
  06-Feb-2023 23:53:22.802 zone_maintenance: managed-keys-zone: enter

This is followup from 3673-delay-trust-anchor-management