First attempt to use LogCapture from testfixtures

This change use LogCapture context manager provided by testfixtures
package.
It provides a way for logging unit testing, better than mock..

Now, `logger` attribute is no longer needed in `ubcommands` classes (and
maybe others..)
Replaced actual logger mocks by LogCapture.
Declared testfixtures as dependency in tox.ini
Added check for abstract adapter logging