tests: Propagate commandline arguments to nose.

This makes it way easier to skip certain tests and to provide other
options specific to nose tests.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
tests: Just skip tests if EC2 env vars are unset.

Now, we shouldn't get assertion errors in case the EC2 environment
variables are not set and can continue running the rest of the tests,
which also include some tests for VirtualBox and also two tests that
don't even require any backend.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
tests: Make logger test discoverable by nose.

By default, nose is only discovering tests if the file name is named
appropriately, so we need to rename the logger test into test_logger.py.

Also, we don't need the import and the test runner in
tests/unit/__init__.py anymore, because it's covered by nose.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
tests: Integrate unit tests into setup.py

We *only* run unit tests here, because we want to avoid running
heavyweight backend specific tests during package installation (which
probably will fail anyway).

Signed-off-by: aszlig <aszlig@redmoonstudios.org>