test: make invalid-option parsing checks portable across platforms

[psumbera]

No description provided.

[wismill]

Thank you for your interest. Could you provide a description and and example where it fails?

[psumbera]

Thank you for your interest. Could you provide a description and and example where it fails?

It fails during tests on Solaris 11.4 like this:

FAIL: test_invalid_option (main.TestXkbcli.test_invalid_option) (tool=XkbcliTool(subtool=None, skipIf=(), skipError=())) 
Traceback (most recent call last):
  File "/builds/psumbera/userland-libxkbcommon/components/x11/lib/libxkbcommon/libxkbcommon-xkbcommon-1.13.1/test/tool-option-parsing.py", line 375, in test_invalid_option
    tool.run_command_unrecognized_option(["--foobar"])
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^
  File "/builds/psumbera/userland-libxkbcommon/components/x11/lib/libxkbcommon/libxkbcommon-xkbcommon-1.13.1/test/tool-option-parsing.py", line 247, in run_command_unrecognized_option
    assert "unrecognized option" in stderr
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError 

[wismill]

Thanks for the MR. Could you improve the commit message so that it explains exactly what it fixes, with an example (e.g. Solaris).

[wismill]

Thanks!