This is only needed for the info method. There is no reason to pollute
the rest of the methods with this.

By default the output goes to sys.stdout. This is used in snf-mkimage
to output the plankton answer when registering an image to a synnefo
deployment.

This resolves #21

The base class is named Output. Having a method with the same makes
the code confusing.

output is a Output class method and using it in _Progress makes the
code more confusing.

According to the decision of the GRNET Board of Directors,
switch license to GPLv3.

This commit will be propagated to the release
and master branches based on git flow, and the next
release will be licensed as GPLv3.

 * Prefix all private methods with _
 * Write missing docstrings
 * Move all public methods above the private ones
 * Add module docstrings where missing
 * Define source code encodings on all modules

If the image gets registered as public allow anyone to read the
metadata and the md5sum file.

Also move it to a separate module.

Logging can be enabled using the -l input option

In the cli output classes this method will clear terminal screen if
the standard output is a terminal.

Also merge data_cleanup tasks with syspreps and did a major cleanup

This can be used to create a set of by default disabled data_cleanup
and sysprep tasks.

* Add foreach_file function in OSBase. This is used by all cleanup
  methods
* Add slackware class. This class derives from linux and overwrites the
  log cleanup behaviour. This is needed since slackware stores all
  package management info in /var/log/packages
* Add a shrink method in DiskDevice. This method shrinks the last
  filesystem to the minimum size
* Make the code style comply with pep8