Add 'allow_duplicate_networks' to compute-feature-enabled options

Nova commit 322cc9336fe6f6fe9b3f0da33c6b26a3e5ea9b0c added the
neutron.allow_duplicate_networks config option in Juno and it defaults
to False. To test it, we need a feature toggle in Tempest so anything
testing against a default Nova setup doesn't fail.

Separate changes will be made to devstack.

Also note Nova change Ideeb3c137ff68a4497189670be33f6edbb0ccb76 which
deprecated the option in Kilo and change
Icb3510bcf0c30e11d0304a86ead91a43f37602ec which removed it in Liberty,
Once kilo-eol happens this is the default behavior in Nova and we can
remove the config option from Tempest.

Related devstack change: Ifd075420f57c9b60746f4a6af6520c0ef04800db
Co-Authored-By: Racha Ben Ali <benali@gmail.com>

Change-Id: I05f81d86cde249c23be06d5804fadbf40fc4a7f3
3 files changed