MAINTAINERS: Add tests/vm entry

Signed-off-by: NFam Zheng <famz@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>

MAINTAINERS

@@ -1905,6 +1905,7 @@ S: Maintained
 F: .travis.yml
 F: .shippable.yml
 F: tests/docker/
+F: tests/vm/
 W: https://travis-ci.org/qemu/qemu
 W: https://app.shippable.com/github/qemu/qemu
 W: http://patchew.org/QEMU/