fix env var

ext/central-controller-docker/main.sh

@@ -79,7 +79,7 @@ echo "{
 }    
 " > /var/lib/zerotier-one/local.conf
 
-until /usr/pgsql-10/bin/pg_isready -h ${ZTC_DB_HOST} -p ${ZTC_DB_PORT}; do
+until /usr/pgsql-10/bin/pg_isready -h ${ZT_DB_HOST} -p ${ZT_DB_PORT}; do
 	echo "Waiting for PostgreSQL...";
 	sleep 2;
 done