Install networking-ofagent from StackForge, using DevStack's
external plugins mechanism.
The following line needs to be added to the existing local.conf settings:
enable_plugin networking-ofagent https://git.openstack.org/stackforge/networking-ofagent
Remove neutron_thirdparty/ryu, as Ryu is installed via
networking-ofagent's requirements.
Change-Id: I12287a47eac4689414f70b517ee37fb98b260e60
Partially-implements: blueprint core-vendor-decomposition
Partial-Bug: #1412653