Add a feature of disabling JVM DNS caching.

see also: https://wiki.apache.org/jmeter/JMeterAndAmazon
Add a feature of using local DNS resolver.

AWS DNS return 8 instance A records, and if ELB has over 8 instance, you can't
use other instances. Because EC2 instances use VPC resolver by default, and
VPC resolver caches ELB instance A records. So, I installed local DS resolver
to avoid VPC DNS resolver cache.
Merge pull request #7 from n3104/disabling_dns_caching

Disabling DNS caching