refactor(makefile): cleanup and add release, dev-release target
refactor(tests): cleanup tests, move common logic into test-setup.sh
chore(tests): add log_phase helper

chore(tests): use log_phase in test-setup

fix(tests): log when testing docs

fix(tests): switch test-smoke to log_phase
fix(tests): install required go dependencies
fix(makefile): replace user-data inline
fix(tests): add DEISCTL_UNITS to test-setup
fix(docs): clean up sources and treat warnings as errors

Many deficiencies in the docs were being skipped over because
`sphinx-build` is lenient. Adding the `-W` flag treats issues
such as "missing reference" and "class not found" as errors.
fix(tests): add correct key to ssh-agent
fix(deisctl): create unit download URL properly after move to subdir
fix(makefile): use portable sed for make discovery-url
Merge pull request #1952 from mboersma/1942-fix-doc-testing

fix(docs): clean up sources and treat warnings as errors
Merge pull request #1951 from gabrtv/make-release

Cleanup Makefile and test suites in preparation for new CD pipeline
Merge pull request #1961 from mboersma/hotfix-unit-urls

fix(deisctl): create unit download URL properly after move to subdir
ref(Vagrantfile): align with upstream coreos-vagrant

See "deis" fork at https://github.com/deis/coreos-vagrant
Merge pull request #1881 from mboersma/update-coreos-vagrant

ref(Vagrantfile): align with upstream coreos-vagrant
ref(tests): move test-nightly to test-latest
Merge pull request #1965 from gabrtv/test-latest

ref(tests): move test-nightly to test-latest