Support tests in Java packages with single identifiers

[tartarughina]

Allow package declarations with a single identifier in addition to
scoped identifiers. Update task commands to handle cases where package
name may be empty.

Address #241

[cla-bot]

Thank you for your pull request and welcome to our community. We could not parse the GitHub identity of the following contributors: Riccardo Strina.
This is most likely caused by a git client misconfiguration; please make sure to:

1. check if your git client is configured with an email to sign commits git config --list | grep email
2. If not, set it up using git config --global user.email email@example.com
3. Make sure that the git commit email is configured in your GitHub account settings, see https://github.com/settings/emails