If the admin network is IPv6 setup the ISC DHCPD server to configure
and use the IPv6 daemon. For this use a seperate set of ipv6 files
to list hosts and subnets as ipv6 hosts and subnets will fail if
v4 dhcp tries to load them.

Also make sure tftp is listening on both IPv4 and v6.

To make this all happen the Network class in the Barclamp::Inventory
library now tracks the ip_version of the network. Which is used to
make decisions through the DHCP and provisioner cookbooks.

To support backwards compatibilty with ipv4 config naming in the
DHCP barclamp a DhcpHelper was added to return config names in
an IPv4 or IPv6 way. The same pattern was used throughout the
barclamp in the early versions of this patch so it's been
refectered to the helper.

Finally, when dealing with some IPv6 addresses in URIs the address
needs to be wrapped. As such the network barclamp has grown a
NetworkHelper module to start gathering network related helper
method's, it's first is a wrap_ip function. Which will wrap an
address if it happens to an IPv6 address. This makes this available
to us anywhere in crowbar, so long as the network barclamp has been
applied, and as a core barclamp to crowbar, should be always.