Add no-constraints job for py37

Some repos, such as reviewstats, use no-constraints jobs since they are
not bound by the same constraints as official OpenStack projects.

This adds a variant using py37 to allow moving beyond the current max
version of py35.

Change-Id: Ibc3aba9e5adffe7a3efab1f4b5bfe7ff48a179b8
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>

zuul.d/project-templates.yaml

@@ -919,6 +919,23 @@
       jobs:
         - publish-openstack-python-branch-tarball
 
+- project-template:
+    name: openstack-python37-jobs-no-constraints
+    description: |
+      Runs the OpenStack PTI jobs for python3.7, but uses the versions of them
+      that do not use constraints.
+    check:
+      jobs:
+        - tox-pep8
+        - tox-py37
+    gate:
+      jobs:
+        - tox-pep8
+        - tox-py37
+    post:
+      jobs:
+        - publish-openstack-python-branch-tarball
+
 - project-template:
     name: openstack-lower-constraints-jobs
     description: |