Include java.net.preferIPv4Stack=true in process startup

I ran into this on a system that didn't have ipv6 disabled. Hadoop started up just fine; however, Accumulo tried to come up but couldn't communicate to itself.

After some netstat investigation, I realized that it bound to the wrong "localhost". We should do like Hadoop and include the -Djava.net.preferIPv4Stack=true java opt when we start Accumulo processes to make things a bit more resilient.