Convert network templates to be rendered via j2

Convert network templates to be rendered via j2

Use the network.network.j2.yaml to render these files, instead
of relying on the hard-coded versions.

Note this doesn't currently consider the _v6 templates as we may want
to deprecate these and instead rely on an ipv6 specific network_data file,
or perhaps make the network/network.network.j2.yaml generic and able to
detect the version from the cidr?

Change-Id: I662e8d0b3737c7807d18c8917bfce1e25baa3d8a
Partially-Implements: blueprint composable-networks