storage: Re-Add logger

In a previous patch the global logger variable got removed to add all
storage related logging output to the logfile, but this change
introduced some other regressions so we are re-adding the original
behavior.

Change-Id: I1da1a5a7687294dbfa895beff2b1f8f14dd4919a
Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>