test: fix test.py command line options processing

https://github.com/nodejs/node/pull/11086 had introduced a regression
that broke command line options processing for tools/test.py.

Basically, it made tools/test.py discard the command line argument that
would be passed after `--abort-on-timeout`. For instance, when running:

```
$ python tools/test.py --abort-on-timeout path/to/some-test
```

all tests would be run because the last command line argument
(`/path/to/some-test`) would be discarded.

This change fixes this regression.

Refs: https://github.com/nodejs/node/pull/11086
PR-URL: https://github.com/nodejs/node/pull/11153


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>