Build without godep

Here's a commit to remove dependency on `godep` when **building** Kubernetes. You still use it to manage to Godeps/ tree.

I'm also reverting the Travis change that pulls `godep` into the CI environment, so Travis will let us know that that works for it too.

I also updated the docs to indicate that `godep` is optional and not required for building.

Cheers,
Filipe

I believe not, because go uses the first item in GOPATH (in this case $KUBE_TARGET which is set to output/go/) to create the pkg/ and bin/ directories...

In my local tests that's what I observed.

But I don't claim to be a GOPATH expert so if someone who knows it better than me could chime in that would be great :-)

Thanks,
Filipe