test: network_mode target causes problem to resolve fqdn names from containers

[lukas-bednar]

When executing network_mode test, it causes for future containers which are being created afterwards.

I hit this issue in PR #51 , the installation of nginx failed on error to resolve nginx.com.
When I execute my test (docker_ports) before executing network_mode everything works ok.

Another problem is that issue persist between runs, the easy fix is restart of docker service.

I think this side effect deserve some attention to be treated properly.

How to reproduce:

• move network_mode in test/Makefile to be executed before docker_ports target

all: cloud inventory docker_inventory docker_cloud groups docker_links docker_volumes_inventory docker_volumes_cloud network_mode docker_ports

• run make

$ make