Switch neutron-tempest-plugin-api job to be ML2/OVN

This patch reverts [1] and switches back to the default networking
backend installed by devstack.

This patch also changes the GRE type networks with VLAN type networks
because of the lack of support.

OVN version is set to v21.03.0. OVN v20.12.0 [2] introduced the support
for ACL log meters (Neutron logging service), but this version is too
old right now.

Partial-Bug: #1928345
Related-Bug: #1929658
Related-Bug: #1914757

[1]https://review.opendev.org/c/openstack/neutron-tempest-plugin/+/791417
[2]https://github.com/ovn-org/ovn/commit/880dca99eaf73db7e783999c29386d03c82093bf

Change-Id: Id087c2a30a7279f9ef9a2c34ddc68a0b11d20c4b
2 files changed