Add experimental job to test upgrades from stein

Also, correct the version that we check out when upgrading from stable
branches.

Change-Id: Ie733bc50466c66d6e6eb5c6bd42e42a05ef88798

.zuul.yaml

@@ -362,6 +362,12 @@
     vars:
       previous_swift_version: origin/stable/rocky
 
+- job:
+    name: swift-multinode-rolling-upgrade-stein
+    parent: swift-multinode-rolling-upgrade
+    vars:
+      previous_swift_version: origin/stable/stein
+
 - job:
     name: swift-tox-lower-constraints
     parent: openstack-tox-lower-constraints
@@ -634,6 +640,7 @@
         - swift-tox-func-ec-centos-7
         - swift-multinode-rolling-upgrade-queens
         - swift-multinode-rolling-upgrade-rocky
+        - swift-multinode-rolling-upgrade-stein
 
     post:
       jobs:

tools/playbooks/multinode_setup/make_rings.yaml

@@ -21,7 +21,13 @@
 
     - name: "checkout a previous version: {{ previous_swift_version | default(latest_swift_release.stdout) }}"
       shell:
-        cmd: git checkout {{ previous_swift_verion | default(latest_swift_release.stdout) }} -b previous_swift_version
+        cmd: git checkout {{ previous_swift_version | default(latest_swift_release.stdout) }} -b previous_swift_version
+        executable: /bin/bash
+        chdir: '{{ zuul.project.src_dir }}'
+
+    - name: confirm checked out version
+      shell:
+        cmd: git describe
         executable: /bin/bash
         chdir: '{{ zuul.project.src_dir }}'