Fix two unittests for PortList.__getitem__().

 * FIXES two unittests which erroneously passed before the previous commit
   which fixed #10333, and then erroneously failed after the fix. They should
   now correctly test indexing the portlist.
Make PortList.__getitem__ unittest more explicit.
Add two unittests for PortList.__getitem__ to debug #10333.
Merge branch 'fix/10333-index-by-0L_r2' into fix/9462-refactor-netstatus-parsers_r9462C_r2