dockertest: Improve the docker logging output

This patchset improves the docker logging output. The output is now easily readable by human eyes and all duplicitous messages were removed. It gets rid of the hacks, which were being used to use autotest-framework logging mechanism and uses the python logging instead (which is default in most of the autotest tests).

The second patch adds flag to set DockerCmd verbosity. In order to be coherent with default autotest rules all commands should be logged. In case of big loops test developer can log the example of code and number of repetition in advance and turn verbose=False. This is preferred for QA guys in order to see, what went wrong without the need to search and analyze the test source code. It's also preferred by feature developers as they never look at autotest sources, they just want to know, what was executed in order to find the problem. Last but not least, better to keep more info and be able to reproduce the exact situation, than miss the problem because test developer didn't expected failure in some part, eg: https://github.com/autotest/virt-test/pull/1497#issuecomment-37375896

This pull request is combination of:
https://github.com/autotest/autotest-docker/pull/27
https://github.com/autotest/autotest-docker/issues/26