Partially revert thin neutron containers

Due to a revert in the Docker code, thin neutron containers do not work
at this time. The neutron plugin agents do not need to exist in the same
container as the other agents however. This allows for using either
linuxbridge or openvswitch

The docker commit that did the revert:
https://github.com/docker/docker/commit/ff770d33cdee5ab4dc0bdeb06dcfea49aa72ab8e

Closes-Bug: 1469307
Change-Id: Idf79c31c74c34b93f5a9bac49730aca49bbdb861