Add project templates for openstack-tox-lower-constraints

Currently many projects use it [1] and in many cases adding requirement
of neutron or horizon. Currently there are other templates that covers
this need for horizon and neutron for other base jobs (e.g. py3*).

This patch adds the following templates for the
openstack-tox-lower-constraints job:

  - openstack-lower-constraints-jobs
  - openstack-lower-constraints-jobs-horizon
  - openstack-lower-constraints-jobs-neutron

[1]:
http://codesearch.openstack.org/?q=-%20openstack-tox-lower-constraints&i=nope&files=&repos=

Change-Id: Ied4fa97755941df31c228b1ec7d7fbecb7ddde66

zuul.d/project-templates.yaml

@@ -567,6 +567,51 @@
       jobs:
         - publish-openstack-python-branch-tarball
 
+- project-template:
+    name: openstack-lower-constraints-jobs
+    description: |
+      Runs openstack-tox-lower-constraints in both the check and gate pipelines.
+    check:
+      jobs:
+        - openstack-tox-lower-constraints
+    gate:
+      jobs:
+        - openstack-tox-lower-constraints
+
+- project-template:
+    name: openstack-lower-constraints-jobs-horizon
+    description: |
+      The standard openstack-lower-constraints-jobs but with horizon added as a
+      required-projects. This checks out the project code and allows
+      tox_install_siblings to use it when building the venv.
+    check:
+      jobs:
+        - openstack-tox-lower-constraints:
+            required-projects:
+              - openstack/horizon
+    gate:
+      jobs:
+        - openstack-tox-lower-constraints:
+            required-projects:
+              - openstack/horizon
+
+- project-template:
+    name: openstack-lower-constraints-jobs-neutron
+    description: |
+      The standard openstack-lower-constraints-jobs but with neutron added as a
+      required-projects. This checks out the project code and allows
+      tox_install_siblings to use it when building the venv.
+    check:
+      jobs:
+        - openstack-tox-lower-constraints:
+            required-projects:
+              - openstack/neutron
+    gate:
+      jobs:
+        - openstack-tox-lower-constraints:
+            required-projects:
+              - openstack/neutron
+
 - project-template:
     name: openstack-pypy-jobs
     check: