[MCLEAN-116] Use default Log interface

[Bukama]

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Provided commit message for squashing

[MCLEAN-116] Use default Log interface
Submitted by: Matthias Bünger

The logging interface of the Cleaner class was not able to log exceptions in a suitable way.
So it was replaced by the default logging interface provided by the AbstractMojo class.

As the AbstractMojo always returns a log instance (therefore never null) the null checks were removed and the same Systemlogger was used in the tests.

As changes are more than 20 lines I will file the icla later the day.

[Bukama]

Additional note aside the commit message: Spotless reformatted a lot in the Cleaner file