RFR: 8213952: Relax DNSName restriction as per RFC 1123

[Seán Coffey]

Looking to make an adjustment to DNSName constructor to help comply with 
RFC 1123

https://bugs.openjdk.java.net/browse/JDK-8213952
http://cr.openjdk.java.net/~coffeys/webrev.8213952/webrev/
regards,
Sean.