FIXES #35: now support multiple composer files

tests/multicompose/d1/docker-compose.yml

@@ -6,4 +6,8 @@ services:
     volumes:
     - ./1.env:/var/www/html/index.txt
     env_file: ./1.env
+    labels:
+      l1: v1
+    environment:
+    - mykey1=myval1
 

tests/multicompose/d2/docker-compose.yml

@@ -2,6 +2,12 @@ version: '3'
 services:
   web1:
     env_file: ./12.env
+    labels:
+    - l1=v2
+    - l2=v2
+    environment:
+        mykey1: myval2
+        mykey2: myval2
 
   web2:
     image: busybox