charm: Add jobs to the gate pipeline

Run the jobs we like before merging a change.

Also, Zuul will not merge a change when the 'gate' pipeline is empty;
And empty pipeline does not equal a successful pipeline run.

Change-Id: I28fdbac6aeb59047ba963ed4b7cbc663508caacb
diff --git a/zuul.d/charm-cinder-storpool-iscsi.yaml b/zuul.d/charm-cinder-storpool-iscsi.yaml
index b1fa8e2..95a4bb2 100644
--- a/zuul.d/charm-cinder-storpool-iscsi.yaml
+++ b/zuul.d/charm-cinder-storpool-iscsi.yaml
@@ -145,6 +145,18 @@
             branches: master
         - zaza-functional-focal-ussuri:
             branches: master
+    gate:
+      jobs:
+        - charm-tox-black:
+            branches: master
+        - charm-tox-pep8:
+            branches: master
+        - charm-tox-lint:
+            branches: master
+        - charm-tox-cover:
+            branches: master
+        - zaza-functional-focal-ussuri:
+            branches: master
     post:
       jobs:
         - publish-to-charmhub: