Neutron Agents json support

Neutron Agents is a special case for json support. Since it's a fat
container, there will be multiple commnds that will need to be run
in the container.  In order to account for this, the commands will be
hardcoded until the agents are split out to their own containers.
The files will be copied the normal way.

Co-Authored-By: Steven Dake <stdake@cisco.com>

Change-Id: I9fc226cc7b82c2594db5814d30d453a29a4af8c0
Partially-Implements: blueprint replace-config-external
Closes-Bug: #1500566