add test process_capabilities_fail

[kazmsk]

This implements the process_capabilities_fail validation in #361

[YJDoc2]

Hey, Thanks for the PR! There is some change needed - basically the current test validates the capabilities call itself fails, i.e. it will error out from line 9. However, we want to check that the container creation itself fails. For this we will need to create a spec with invalid value, and then assert that the container creation has failed.

For this, what we can do is this -

• create a valid spec, with a single valid capacity
• then use this spec with test_inside_container
  • here you'll need to update the code of test_inside_container in test_utils:204 to return error instead of calling unwrap.
  • In the function call, we get to provide a callback function which runs right before the container is created. This fn gets the rootfs path as a param. The spec (named config.json) it right outside the rootfs files for our tests, so you can edit the path to get the spec string, replace the cap name with an invalid name and re-write it there. Now we will have an invalid spec.
• With this, you can check that the test_inside_container fails because of the capabilities issue.

Please let me know if the above explanation is not clear/ you need any help.