Add BGPVPN services to scenario004

Add BGPVPN services to scenario004

This submission will enable the BGPVPN API
on scenario004.

This addition to scenario004 does not
provide any sanity check for the Neutron API
extension. At this stage is meant to
install the required packages and prerequisites,
configure the extension and
having the services started correctly.

In the README.rst file, this is displayed as
neutron-bgpvpn, so for further integrations
should be added as neutron-<extension_name>
for an easier reading.

Depends-On: I4d0617b0d7801426ea6827e70f5f31f10bbcc038
Depends-On: I2be0fab671ec1a804d029afc6dc27d19a193b064
Change-Id: I6c257417a9231c44e13535bc408d67d2a3cacbf8