Generalize where* functions

[md5]

This PR generalizes the where* functions to allow an array or slice of any map or struct type.

This should make it possible to fix nginx-proxy/nginx-proxy#115 since the updated where function can be used like this: {{where (where $container.Addresses "Proto" "tcp") "Port" "80" | len}} to detect the case where there are multiple ports exposed but not port 80.

I also introduced a templateTestList type with a run function to simplify writing tests that actually execute a template and check its output. Let me know if you'd like that split into a separate PR.

[md5]

Looks like os.Unsetenv is only in Go 1.4+, causing the Travis failure. I've changed it to os.Setenv("DOCKER_HOST","")

[thaJeztah]

Are there blockers for Go 1.4 in docker-gen, or are people importing it in other projects? Perhaps 1.4 isn't a bad thing to use (Docker, for example, very recently dropped 1.3 support)

[md5]

Good point @thaJeztah.

[jwilder]

I don't see any reason to keep 1.3 around. docker-gen isn't really intended to be used as a library right now so it should not matter if the code is dependent on 1.4 features.

[md5]

@jwilder I've dropped commit 844fa87, so the Travis build now fails again on 1.3.

[jwilder]

@md5 I removed 1.3 from travis. If you rebase, it should pass now.

[md5]

Rebased. Travis is green 👍

[jwilder]

Thanks @md5!

[md5]

You're welcome! 👍