[neutron-tempest-plugin] Tag train-last

Train branch is in Extended Maintenance now[1]. Tempest and
tempest plugins are branchless which means master version of
Tempest and its plugins is used to test the supported stable
branches.

Once any stable branch is moved to EM state then, Tempest and
its plugins compatible tag[2] needs to be released so that we can
keep testing the EM stable branches with that tag once master
Tempest and its plugins are not compatible[3].

Tagging 'train-last'[4] as well as a new version also with same hash.

[1] https://releases.openstack.org/train/index.html
[2] https://docs.openstack.org/tempest/latest/stable_branch_support_policy.html
[3] https://docs.openstack.org/tempest/latest/tempest_and_plugins_compatible_version_policy.html
[4] https://docs.openstack.org/project-team-guide/stable-branches.html#extended-maintenance

Change-Id: I2f65701ebf6a7916f7c72457ae0bd6531b57608a

deliverables/train/neutron-tempest-plugin.yaml

@@ -21,3 +21,7 @@ releases:
     projects:
       - repo: openstack/neutron-tempest-plugin
         hash: 3a4fc7923efe21a7f56ba130f05efdfcd3c596ec
+  - version: train-last
+    projects:
+      - repo: openstack/neutron-tempest-plugin
+        hash: c55bd059edb990454eba01f512fc40d09d02db26

deliverables/xena/neutron-tempest-plugin.yaml

@@ -14,3 +14,7 @@ releases:
     projects:
       - repo: openstack/neutron-tempest-plugin
         hash: 887f5ac7303a016feeba5b926e4a63a5ef2ced65
+  - version: 1.6.0
+    projects:
+      - repo: openstack/neutron-tempest-plugin
+        hash: c55bd059edb990454eba01f512fc40d09d02db26