Validation when adding a registry

[bradrydzewski]

The add registry endpoint expects a hostname only and should reject any values with special characters such as slashes. Otherwise they cannot be deleted.

[shivamMg]

@bradrydzewski There's a nice hostname validator in goa framework. Their validators do not come in a separate package though; so to use them we'll have to import entire goa package. If it seems superfluous we can implement it ourselves. They've linked the RFC they used for creating that regex: https://www.ietf.org/rfc/rfc1035.txt (Page 7).

[shivamMg]

Used IsHost validator from govalidator instead. The one in goa is just for <label> from the RFC, and not for <domain>. Regex for domain becomes pretty complex. Also an IP can also be a possible registry address.

[bradrydzewski]

Merged into 0.9 release. Pending verification.