Fix broken ipv6 address verification in salt.utils.validate.net

Because of https://github.com/saltstack/salt/commit/37af3acfe8ea3178b8fc660076c723ad5694bedc some tiny sweet cats must cry because in their opinion

1. It's absolutely nonsense to have regular expressions that nobody can understand and maintain
2. It's wrong to reinvent the wheel, so using the socket package would have been sufficient
3. It's wrong to change this validation process without knowing whether it will work or not due to not adding any tests

See here for sad cats: http://lmgtfy.com/?q=sad+cat


Also the current implementation of the ipv6_addr tells us that ``2a03:4000:c:10aa:1017:f00d:aaaa:a`` is not a valid IPv6 address. This is not true and breaks (in my case) salt.states.network.managed().


To make both functions less error-prone and less annoying I propose the following patch. 


See here for happy cats: http://lmgtfy.com/?q=happy+cat
I never understood why this check (L46) should be meaningful. If it is, please get me to know it.