Bugfix: Ignore return value with command option

We were ignoring a return value of the program we executed with --command flag. This release fixes that and it also adds an optional argument where ignoring program return value is expected behavior (then warnings are parsed and decision is taken on that).

Be aware that ignoring command return value can have a side effect where command fails, does not produce any output, therefor there are no warnings, so plugin marks it as passed.