fix: test: Wait for "all zones loaded" after rndc reload in "database" test

After the rndc reload command finished, we might have queried the
database zone sooner than it was reloaded because rndc reloads zones
asynchronously if no specific zone was provided. We should wait for "all
zones loaded" in the ns1 log to be sure.

Closes #5075

Merge branch '5075-database-rndc-reload-ensure-all-zones-loaded' into 'main'

See merge request isc-projects/bind9!9829