Group name validator

[dieu]

FormatSharedNamesAndAppendUniqueStringToThoseWhichRepeat.java

private Validator<String> groupValidator = new DnsNameValidator(3, 63);

Why now for the validation group name used DnsNameValidator? because of this, you can not use the name in uppercase

[codefromthecrypt]

because jclouds intends to be compatible with multiple cloud providers and
some use dns for the names.

[jclouds]

you could probably rename this to "make it possible to override group name
validator". It is more important to be able to override than to undo the
default, right?

[dieu]

@adriancole yep, I would like implementing Cloud specific validator.