[role:glance] Update worker number as 8

Default value was 1.
diff --git a/roles/openstack_helm_glance/vars/main.yml b/roles/openstack_helm_glance/vars/main.yml
index d0d586f..7bb4fbd 100644
--- a/roles/openstack_helm_glance/vars/main.yml
+++ b/roles/openstack_helm_glance/vars/main.yml
@@ -54,6 +54,7 @@
         show_image_direct_url: true
         show_multiple_locations: true
         enable_import_methods: "[]"
+        workers: 8
       cors:
         allowed_origins: "*"
       image_formats: