features: Rename 'step_definitions' to 'steps'

Signed-off-by: Jussi Virtanen <jussi.k.virtanen@gmail.com>
features: Rename 'I run' to 'I run command'

Aruba provides a more general 'I run' step. Rename pstore's 'I run' step
to 'I run command' to prevent ambiguity.

Signed-off-by: Jussi Virtanen <jussi.k.virtanen@gmail.com>
features: Depend on 'aruba'

Signed-off-by: Jussi Virtanen <jussi.k.virtanen@gmail.com>