Fix neutron packaging

Update openstack-neutron specfile to make RPM really buildable and
installable:
- package backward-compatibility python module;
- take into account that some executables were not renamed;
- add subpackages for Mellanox and ML2 plugins;
- minor spec adjustment to reflect neutron changes.

Partial-bug: #1198041
Change-Id: Ie7e73aefba29b9a2c181dea02050690e5c727c26
Merge "Fix neutron packaging"