Neutron: start to use nova's neutron configuration section

Commit 5cacad3508570ce70b1f9ef620e0508169687fda added support
of a neutron section. This updates the code to make use of
that section.

Change-Id: I86119476fde5066182d3aadcee5985019202647a
Merge "Neutron: start to use nova's neutron configuration section"
Merge branch 'master' of github.com:openstack-dev/devstack