BREAKING CHANGE: `cli-plugin-unit-jest` and `cli-plugin-unit-mocha` now register
"test:unit" command and script instead of "test"; `cli-plugin-e2e-cypress` now
register "test:e2e" with optional `--headless` flag instead of "e2e" and
"e2e:open"; `cli-plugin-e2e-nightwatch` now register "test:e2e" instead of "e2e".
close#876, close#878