add 'via' matcher

[trombik]

tcpdump -i any is supported only on Linux kernel. adding via is just a work around but better than nothing.

describe server(:fluentd1) do
  describe firewall(server(:fluentd1)) do
    it { is_expected.to be_reachable.via('lo0').dest_port(24284) }
  end 
end

[coveralls]

Coverage decreased (-0.9%) to 79.43% when pulling f5e831b on trombik:interface into 006ba3b on otahi:master.

[coveralls]

Coverage decreased (-0.9%) to 79.375% when pulling ad41ae0 on trombik:interface into 006ba3b on otahi:master.

[otahi]

@trombik Thank you for your pull request.
I agree with you basically, so I think I want to merge this pull request.

I have 2 points to indicate.

1. I think dest_interface is more suitable in this situation than via, because there are dest_interface and src_interface(But I know you don't mention about src_interface in this case)
2. Please add some integration tests(unit tests are also OK if you think unit tests are better.)

Please give your thoughts, or questions to me.
Thank you,

[trombik]

via was chosen because it sounds more like spoken English. but that is not a deal breaker. as for unit tests, fair enough. however, it would take some time for me to dive into rspec. let me give it a try

[otahi]

@trombik Thank you for your trying.

via sounds nice for me too, but now via is used for firewalls like this.

$ bundle exec rspec

server 'src'
  via firewall
    should reach to server 'dst'

So, we had better to change to some other words. I think.

Please feel free to contact me if you have something.