Add dependencies inside docker dinamically

[i4ki]

My problem:

• I don't want to have the go dependencies hardcode inside the Dockerfile;
• I don't want to execute "go get -d ./..." in every "make check" because it slows down the code-test flow.

Solution:

I create a new script hack/gendeps.sh executed by Makefile that generates a file hack/deps.txt when it do not exists and added hack/deps.sh inside the dev docker. The hack/deps.sh works for Dockerfile or to solve dependencies manually in the host.

This approach doesn't seem good but solves my current problem.

@katcipis Could you test if this PR works in your env?

What's the best way to achieve that?

[coveralls]

Coverage remained the same at 46.77% when pulling 79a97c500a582778b2715f667053579b6e2f08ca on tiago4orion:env-deps into b506dd227d618bb508da88045606f60d2b997195 on NeowayLabs:master.

[coveralls]

Coverage remained the same at 46.77% when pulling 99b7b6a399869a88e7845eaafe4a0e39a7727b7c on tiago4orion:env-deps into b506dd227d618bb508da88045606f60d2b997195 on NeowayLabs:master.