Fix NoMethodError bugs in docker::aufs recipe

[trinitronx]

Fixing some bugs introduced in #35:

NoMethodError
-------------
undefined method `empty?' for nil:NilClass '`

NoMethodError
-------------
undefined method `Version' for Gem:Module`

Tests passing via:

1. bundle exec kitchen test ubuntu
2. bundle exec foodcritic .
3. bundle exec rubocop
4. bundle exec knife cookbook test

Note: fedora-19 currently has a problem running the docker tests, but
this was already happening before #35. Please see this gist

[bflad]

Thanks for the fixes, this will be released in 0.23.1 (just pushed 0.23.0).

[jayofdoom]

Sorry about this; I thought .empty? just returned False in a nil situation.

[trinitronx]

@jayofdoom yeah no problem, I've made the same mistake before ;-)

👍 on the handling of the aufs package edge case