Guard against writing test modules in the build / dist output

TestModule in testsuite/shared will create modules without adequately checking that it's not writing in the shared modules folder from [something-]build/target or [something-]dist/target.

If module.path is configured, it should prefer the first path element not in such a dir. If there is no such path, it should fail.

If module.path is not configured it should confirm that jboss.home does not point to such a dir and fail if it does.