Remove old cucumber test infrastructure
Handle version conflicts in Maestro.best_version
Maestro.best_version: Filter out None values before determining top requirements
Deal with second-level requirements without version info

The method `Maestro.best_version()` didn't know how to deal with
second-level dependencies without version info;

Meaning that it would explode if we received a request like this:

  >>> request_install('pacakge', dependency_of='pkg (x.y.z)')

Instead of something like this:

  >>> request_install('pacakge (x.y.z)', dependency_of='pkg (x.y.z)')
Decrease size of test names in test_maestro.py by removing unnecessary suffix