Return non-zero for bad or insufficient parameters
Merge pull request #696 from gasull/exit-status-ubuntu-installer

Return non-zero for bad or insufficient parameters
Deactivate bad unused import.

* ebaysdk missing from project requirements.
Enable pylint imports check (F0401).
Do not pylint inside html/bower_components.
Subpackage db and test folders.

* Effectively allows relative imports from/to these folders.
Fix broken imports in the db, features and test packages.
Locally disable import errors.

* Unable to import distutils.utils in Travis CI.
Disallow wildcard imports (W0401).

* Also flag unused names from wildcard imports (W0614).
Refactor wildcard imports.

* Drop wildcard; state imported names explicitly.
* Import each module only once.
* Drop unused imports.
* Fix broken imports: Explicitly import modules
  previously implicitly imported by wildcard.