Different ways to add construct the procfile slice for goreman

Created by: lahiguera

I'm studying Sourcegraph source code.

Looking at cmd/server/shared/shared.go I saw some different ways to determine what to append to the procfile slice that will be used as an argument for goreman to run. Some of them checked that length is different from 0, some used variables with scope local to an if.

I thought I could make that a little bit uniform and use this as a simple contribution.