spec_helper: improve coveralls + simplecov handling

Load and start coveralls only if the tests are executed by travis (CI
environment variable).

With ENV['COVERAGE'] run simplecov directly.
dpkg: remove unused method
use logger class for output

Replace all puts calls with call of an own logger class. This way is more
extentable, it is clear that it is no debug output and the output can be
disabled inside of test runs.
lib: improve require order/position
recipe: add depend method #3
dpkg: use spec dependencies inside creator #3