[MPMD-171] Rule properties are ignored when run under MPMD - unit test

Just a unit test for https://jira.codehaus.org/browse/MPMD-171
Couldn't reproduce it anymore. The issue was probably fixed with PMD 5.0.3/5.0.4.
The bug report is for m-pmd-p 3.0.1, which uses PMD 5.0.2.

Related bugs are: https://sourceforge.net/p/pmd/bugs/1074/ (rule priority doesn't work on group definitions) and https://sourceforge.net/p/pmd/bugs/1089/ (When changing priority in a custom ruleset, violations reported twice)