Add metadata proxy L3 agent driver

To-Do:
* vArmourL3NATAgent (Before this patch) overrides _spawn/destroy_metadata_proxy
  with empty stubs. This behavior should be maintained so that the metadata proxy
  is not created when using vArmourL3NATAgent. It also overrides _router_added
  and _router_removed, causing L3 agent driver notifications to not send out.

Partially-implements: blueprint restructure-l3-agent
Change-Id: I36900b02bff34269f789956aa324379ff51eb81b
Remove NSX 'service' plugin

Following the spin-off for Neutron advanced services, this plugin
has become non-functional.
This patch removes the plugin, the service drivers, the database
models which kept tracking of resource associations, exceptions,
and obviously unit tests.

As there were some extensions which were leveraged only by this
plugin, they are being removed as well. In particular, one of
these extensions, 'routed-service-insertion' was in the
neutron.extensions package rather than neutron.plugins.vmware
package. This was for historical reasons. As no other plugin is
using this extension, it is being removed as well with this
patch.

By removing this plugin vmware the temporary skips applied to
neutron unit tests can be lifted. This patch does this.

Closes-Bug: #1403585

Change-Id: I0717f955b0f787c2951cb9db44ea5decc5d3dff0
Merge "Add metadata proxy L3 agent driver"
Merge "Remove NSX 'service' plugin"