use godep for builds

[mreiferson]

this is one option for addressing the reproducible build problem. I personally find it to be a simple, elegant, solution. See more information at https://github.com/kr/godep

[mreiferson]

Unfortunately, without jumping through hoops, godep does not support go1.0.3, see tools/godep#7

Gonna need to see how that resolves before proceeding...

[mreiferson]

OK, to update this PR, the idea is that we'd like to move forward and get this in despite the fact that upstream changes have once again caused issues building godep with go1.0.x.

End users have a few options...

1. download our pre-built binaries for the OS/arch/go version
2. one-liner patch code.google.com/p/go.tools/go/vcs like we do in the .travis.yml in this PR and then build and use godep
3. satisfy the dependencies and build manually using the revisions listed in the Godeps file (building NSQ binaries doesn't require godep, just our makefile and shell scripts won't be usable)

So really this change primarily affects developers of NSQ, not end-users.

[mreiferson]

merge me @jehiah