The get_format() method allows to check which compression format
a given input stream has. This is done by calling the supported
compression tools in a row and let them check if they can deal
with the provided data or not. As a result error messages are
logged for streams that some tool doesn't understand. However,
those error messages are no errors and only the result of the
checking. This information in the kiwi log file is confusing
and several users already complained when they see information
like:
EXEC: Failed with stderr: /usr/bin/xz: ...: File format not recognized
This commit changes how the compression tooling is called in a
way that no exception is raised (which leads to the above error message)
but the result returncode is used to decide on the success or
error of the respective compression tooling.
0b13c48c21