hs-test: use anchors in yaml config files

Volumes can be referenced with anchors to reduce text duplication
and to explicitly show which containers share a volume.

Type: test
Signed-off-by: Maros Ondrejicka <maros.ondrejicka@pantheon.tech>
Change-Id: Id408a78262573b3faf2257c32bfa569eca2e2049
diff --git a/extras/hs-test/topo-containers/single.yaml b/extras/hs-test/topo-containers/single.yaml
index e0fea70..9ecdc90 100644
--- a/extras/hs-test/topo-containers/single.yaml
+++ b/extras/hs-test/topo-containers/single.yaml
@@ -1,17 +1,18 @@
 ---
 volumes:
-  - shared-vol
+  - volume: &shared-vol
+      host-dir: shared-vol
 
 containers:
   - name: "vpp"
     volumes:
-      - host-dir: "shared-vol"
+      - <<: *shared-vol
         container-dir: "/tmp/vpp"
         is-default-work-dir: true
   - name: "nginx"
     volumes:
-      - host-dir: "shared-vol"
+      - <<: *shared-vol
         container-dir: "/tmp/nginx"
         is-default-work-dir: true
     image: "hs-test/nginx-ldp"
-    is-optional: true
\ No newline at end of file
+    is-optional: true