Previously exported as 'vpc_cidr' and removed when preexisting vpc usage
was added. This config data is used on local.params and was mentioned on the
documentation page.
Now, it's exported as 'cluster_int_cidr' and its value is requested from AWS
so that we get the correct one whether the vpc was just created or a
previously existing one is being in use.
Arvados-DCO-1.1-Signed-off-by: Lucas Di Pentima <lucas.dipentima@curii.com>