Slow down counter updates to avoid timeouts
Slow down counter updates to avoid timeouts

This should help prevent global_row_key_cache_test from failing
with a write timeout against 2.0

iamaleksey/cassandra-dtest,mambocab/cassandra-dtest,pauloricardomg/cassandra-dtest,beobal/cassandra-dtest,snazy/cassandra-dtest,carlyeks/cassandra-dtest,snazy/cassandra-dtest,stef1927/cassandra-dtest,mambocab/cassandra-dtest,pcmanus/cassandra-dtest,riptano/cassandra-dtest,krummas/cassandra-dtest,tjake/cassandra-dtest,krummas/cassandra-dtest,bdeggleston/cassandra-dtest,pauloricardomg/cassandra-dtest,blerer/cassandra-dtest,thobbs/cassandra-dtest,riptano/cassandra-dtest,stef1927/cassandra-dtest,spodkowinski/cassandra-dtest,thobbs/cassandra-dtest,blerer/cassandra-dtest,bdeggleston/cassandra-dtest,aweisberg/cassandra-dtest,iamaleksey/cassandra-dtest,carlyeks/cassandra-dtest,aweisberg/cassandra-dtest,beobal/cassandra-dtest,spodkowinski/cassandra-dtest