Fix flaky unit test in `MetaFilterBehaviour`

Unit tests MetaFilterBehaviour.shouldParseIncludesAndExcludesUsingDefaultMetaMatcher fails because of order of items in String generated by Properties.toString() :

MetaFilterBehaviour.shouldParseIncludesAndExcludesUsingDefaultMetaMatcher: 

Expected: "{author=Mauro, defect-4321=, map=*API}"

     but: was "{defect-4321=, author=Mauro, map=*API}"

MetaFilterBehaviour.shouldParseIncludesAndExcludesUsingDefaultMetaMatcher:

Expected: "{defect-1234=, theme=smoke testing, skip=}"

     but: was "{defect-1234=, skip=, theme=smoke testing}"