Refactor and test [github] token persistence (#1863)

lib/github-auth.js

lib/in-process-server-test-helpers.js

lib/service-test-runner/cli.js

lib/text-formatters.spec.js

lib/token-persistence.js

lib/token-persistence.spec.js

package-lock.json

package.json

server.js

services/github/github-constellation.js