Added validator for site infrastructure

[snehasi]

Hi,

I've added validator for site infrastructure, fixing #4.

We had to validate two fields - fqdn and ipv4 address - for the schema.

For fqdn, instead of going with a custom regex, I've used fqdn module from pypi as it implements fqdn validation fully compliant with RFC-1035 making it more robust.

For ip4 address, I've used yamale's built-in ip validator.

Looking forward to reviews on the PR.

[maany]

Cool, I've tested the PR. It works well :) The task for GSoC is complete. I'll incorporate the PR into the code later.