Zuul: support plugin dependencies

Change-Id: I81302e8988fe6498fea9f08ed66f5d0cc1fce161
diff --git a/roles/write-devstack-local-conf/tasks/main.yaml b/roles/write-devstack-local-conf/tasks/main.yaml
index cc21426..2a9f898 100644
--- a/roles/write-devstack-local-conf/tasks/main.yaml
+++ b/roles/write-devstack-local-conf/tasks/main.yaml
@@ -8,3 +8,4 @@
     services: "{{ devstack_services|default(omit) }}"
     localrc: "{{ devstack_localrc|default(omit) }}"
     local_conf: "{{ devstack_local_conf|default(omit) }}"
+    base_dir: "{{ devstack_base_dir|default(omit) }}"