increase bin/solr's post kill sleep

Currently e.g. https://github.com/apache/lucene-solr/blob/releases/lucene-solr/8.5.1/solr/bin/solr#L863 we wait for one second after the kill -9 before re-checking if the process still exists.

We've seen a few cases where the kill -9 succeeded but only slightly after the one second interval. So this ticket here proposes to increase the interval from 1s to (say) 10s.