Validate vhosts names more strictly

There was a bug in the setup page where valid domains that start with a number
would be captured by the validation check designed to detect IP
addresses. This check detects IPs by comparing the host name to a regex,
instead of simply detecting whether the first character is a number.
Improve IP detection regex so it isn't fooled by domains that
look like IP addresses.
Merge pull request #488 from lucaswilric/ip-regex

Validate vhosts names more strictly