Fix manila tempest plugin issue in W/V

Manila's devstack plugin can be told not to install
the manila tempest plugin hostwide. Installing the
plugin host-wide isn't reqired and would cause issues
with requirements for other packages.

The same change has been merged in python-tempestconf:
https://review.opendev.org/c/openinfra/python-tempestconf/+/854213

Change-Id: Id3876ad8d2a09e8fbad4834880186d55bb1d10da

.zuul.yaml

@@ -100,9 +100,8 @@
     override-checkout: stable/wallaby
     vars:
       branch: stable/wallaby
-    required-projects: &manila-tempest-plugin-pin
-      - name: openstack/manila-tempest-plugin
-        override-checkout: 1.8.0
+      devstack_localrc:
+        MANILA_INSTALL_TEMPEST_PLUGIN_SYSTEMWIDE: false
 
 - job:
     name: refstack-client-devstack-victoria
@@ -110,4 +109,5 @@
     override-checkout: stable/victoria
     vars:
       branch: stable/victoria
-    required-projects: *manila-tempest-plugin-pin
+      devstack_localrc:
+        MANILA_INSTALL_TEMPEST_PLUGIN_SYSTEMWIDE: false