setup-devstack-source-dirs: add var for paths

The paths for the devstack source directories are currently hardcoded,
this patch allows overriding that list.

Change-Id: I2b673b0d110d84658b89bb14663584330deaf3aa

roles/setup-devstack-source-dirs/defaults/main.yaml

@@ -1 +1,9 @@
 devstack_base_dir: /opt/stack
+devstack_source_dirs:
+  - src/opendev.org/opendev
+  - src/opendev.org/openstack
+  - src/opendev.org/openstack-dev
+  - src/opendev.org/openstack-infra
+  - src/opendev.org/starlingx
+  - src/opendev.org/x
+  - src/opendev.org/zuul

roles/setup-devstack-source-dirs/tasks/main.yaml

@@ -1,13 +1,6 @@
 - name: Find all OpenStack source repos used by this job
   find:
-    paths:
-      - src/opendev.org/opendev
-      - src/opendev.org/openstack
-      - src/opendev.org/openstack-dev
-      - src/opendev.org/openstack-infra
-      - src/opendev.org/starlingx
-      - src/opendev.org/x
-      - src/opendev.org/zuul
+    paths: "{{ devstack_source_dirs }}"
     file_type: directory
   register: found_repos