Fail when Nova API, Nova network and Swift hosts are not set as IP addresses

- Refactor value validator system - cleanup, pep8, documentation, tests and allow multiple validators for each parameter

Fixes: rhbz#886603

Change-Id: I1bb3486ed7168bda2855ee877e32423033620ecc
Merge "Fail when Nova API, Nova network and Swift hosts are not set as IP addresses"