Add py37 func test job

Make a new func-py3 tox env that will use whatever version of py3 is
available, and set up a new check/gate job that runs it under py37.

Change-Id: I1ef233276697be994494ed858e88ce97634f814e

.zuul.yaml

@@ -81,6 +81,21 @@
     vars:
       tox_envlist: func
 
+- job:
+    name: swift-tox-func-py37
+    parent: swift-tox-base
+    nodeset: ubuntu-bionic
+    description: |
+      Run functional tests for swift under cPython version 3.7.
+
+      Uses tox with the ``func-py3`` environment.
+      It sets TMPDIR to an XFS mount point created via
+      tools/test-setup.sh.
+    vars:
+      tox_envlist: func-py3
+      bindep_profile: test py37
+      python_version: 3.7
+
 - job:
     name: swift-tox-func-centos-7
     parent: swift-tox-func
@@ -369,6 +384,11 @@
               - ^(api-ref|doc|releasenotes)/.*$
               - ^test/probe/.*$
               - ^(.gitreview|.mailmap|AUTHORS|CHANGELOG)$
+        - swift-tox-func-py37:
+            irrelevant-files:
+              - ^(api-ref|doc|releasenotes)/.*$
+              - ^test/probe/.*$
+              - ^(.gitreview|.mailmap|AUTHORS|CHANGELOG)$
         - swift-tox-func-encryption:
             irrelevant-files:
               - ^(api-ref|doc|releasenotes)/.*$
@@ -439,6 +459,7 @@
         - swift-tox-py27
         - swift-tox-py37
         - swift-tox-func
+        - swift-tox-func-py37
         - swift-tox-func-encryption
         - swift-tox-func-domain-remap-staticweb
         - swift-tox-func-ec