Move Zuul jobs in-tree

Convert the tox jobs to Zuul v3 native and move them here.

Use tox environment instead of openstack-tox since upper-constraint
is not needed.

Change-Id: Ic933cf202d20625e692c9ec40584ca6bc12f7da5
Needed-By: Ie295a23c5921e9213ccef31367d642eec2288ef3

.zuul.yaml

@@ -0,0 +1,29 @@
+- project:
+    check:
+      jobs:
+        - requests-mock-keystoneclient-tip
+        - requests-mock-novaclient-tip
+    gate:
+      jobs:
+        - requests-mock-keystoneclient-tip
+        - requests-mock-novaclient-tip
+
+- job:
+    name: requests-mock-keystoneclient-tip
+    parent: tox
+    description: |
+      Run test for requests-mock project.
+
+      Uses tox with the ``keystoneclient-tip`` environment.
+    vars:
+      tox_envlist: keystoneclient-tip
+
+- job:
+    name: requests-mock-novaclient-tip
+    parent: tox
+    description: |
+      Run test for requests-mock project.
+
+      Uses tox with the ``novaclient-tip`` environment.
+    vars:
+      tox_envlist: novaclient-tip