CI: make sure old swift is truly gone for rolling-upgrade jobs

While switching how some executable scripts were configured, I saw
some strange rolling-upgrade failures that seemed to indicate that
the new invocation method was trying to be used with old code. It
seems like it maybe has something to do with whether swift was
installed to /usr/local/lib/python3.9/site-packages/ or
/usr/local/lib64/python3.9/site-packages/ but I'm not entirely
sure.

At any rate, a proper package manager ought to uninstall the old
version then install the new one, so it seems reasonable to do that
with pip, too.

Change-Id: I12e84745e7601d162755bc9d0f1cda7b63e92197

tools/playbooks/multinode_setup/run.yaml

@@ -13,6 +13,13 @@
 - hosts: storage
   tasks:
 
+    - name: remove old swift
+      become: true
+      shell:
+        cmd: pip uninstall -y swift
+        executable: /bin/bash
+        chdir: '{{ zuul.project.src_dir }}'
+
     - name: checkout master swift
       shell:
         cmd: git checkout master