I don't think this is necessary. You can override the default of "src/it" with something like:
<projects> <!-- configure test mojo to run foo/*/pom.xml -->
<filesets> <!-- configure clean mojo to delete bar and all its contents -->
If a user wants to override one of these, it seems likely they're doing something unconventional and would want to override both explicitly.
I do think the element names <projects> and <filesets> are a bit unintuitive, though...