iotests: Test 041 only works on certain systems

041 works fine on Linux, FreeBSD, NetBSD and OpenBSD, but fails on macOS.
Let's mark it as only supported on the systems where we know that it is
working fine.

Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-id: 20200121095205.26323-3-thuth@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>

tests/qemu-iotests/041

@@ -1134,4 +1134,5 @@ class TestOrphanedSource(iotests.QMPTestCase):
 
 if __name__ == '__main__':
     iotests.main(supported_fmts=['qcow2', 'qed'],
-                 supported_protocols=['file'])
+                 supported_protocols=['file'],
+                 supported_platforms=['linux', 'freebsd', 'netbsd', 'openbsd'])