OS-438, [v3] IPv6 support for Infoblox

Code was rebased
Actually we can't rely on ('-6' not in cmdline)  since dhcprelay path can be changed by user from config.
We should parse cmd line or at least exclude dhcprelay path from it.
With your patch we will have guaranted order of arguments and '-4' or '-6' goes right after dhc_relay path:
[self.conf.dhcrelay_path, '-4', '-a', '-i', self.interface_name]
So you can check if cmdline starts with 'self.conf.dhcrelay_path', after it check next two characters, they will be '-4' or '-6' and then check if self.interface_name is present in part that left.