Add exception handler for role networks
Add exception handler for role networks

When a role network is undefined, or otherwise unknown, we need to raise
a warning but allow the generation to continue.

Signed-off-by: Kevin Carter <1d9a750a4fc7026fb02029431dc8a87d24487135@redhat.com>
Change-Id: I2d9709e057dc1c818afbadebba79889e6447e836

openstack/tripleo-common,openstack/tripleo-common