Fix hostname validation

hostnames can be up to 49 characters in length. They can contain the letters A-Z or a-z, numbers 0-9 and special character – (dash), and the period (.).

Basic Hostname Guidelines: A hostname cannot have any spaces, nor can it start with a dash.

Valid examples:

• domaindotcom
• domain-dotcom
• domain123-com
• my123.domain-123.com123
• my-123-domain.com-123
• 123my.do-main.com