add Docker to build VM temlates

Now Docker is installed to VM which are used to build Maxscale. It allows to run tests which require Docker without installing it
during build process.

BUILD/mdbci/templates/build.json.template

@@ -3,7 +3,11 @@
   {
         "hostname" : "default",
         "memory_size" : "4096",
-        "box" : "$box"
+        "box" : "$box",
+        "product" : {
+                "name": "docker"
+        }
+
   }
 }