tests: factor out base nginx-proxy config

test/test_default-host/test_default-host.yml

@@ -1,5 +1,8 @@
 services:
-  # GIVEN a webserver with VIRTUAL_HOST set to web1.tld
+  nginx-proxy:
+    environment:
+      DEFAULT_HOST: web1.tld
+
   web1:
     image: web
     expose:
@@ -7,11 +10,3 @@ services:
     environment:
       WEB_PORTS: "81"
       VIRTUAL_HOST: web1.tld
-
-  # WHEN nginx-proxy runs with DEFAULT_HOST set to web1.tld
-  sut:
-    image: nginxproxy/nginx-proxy:test
-    volumes:
-      - /var/run/docker.sock:/tmp/docker.sock:ro
-    environment:
-      DEFAULT_HOST: web1.tld