Enable depman to not require a default branch for deps, run go fmt, fix imports

Acceptance criteria:
- If a version is not specified in deps.json for a given dependency, depman is expected to pick the default trunk branch for the VCS specified. Thus, for the following Git dependency, depman will try to assume a value of "master" for the missing version:
{
  "someArtifact": {
    "repo": "ssh://git@git.myrepo.com/some/Artifact.git",
    "alias": "sa",
    "type": "git-clone"
  }
}

- If go fmt is run against the code in this request, it should find no files to correct.