Support more tools in XML comparator

Currently xml comparator (xml.py) use only minidom for comparing xml, which currently fail for invalid xml files, see issues #165

below list of additional commands that can be used to format xml (they should work on invalid data as well)

related packages in debian are: python3-tidylib xmlformat-perl xmlformat-ruby

libxml2-utils (command: xmllint --format)

xmlstarlet (command: xmlstarlet fo)

options from python code (without invocation of command) https://stackoverflow.com/questions/749796/pretty-printing-xml-in-python