Update https://github.com/kata-containers/documentation/blob/master/.ci/test-install-docs.sh so that:

• after the test the Kata packages are removed.
• the following docs are also tested:
  • https://github.com/kata-containers/documentation/blob/master/install/installing-with-kata-doc-to-script.md
  • https://github.com/kata-containers/documentation/blob/master/install/installing-with-kata-manager.md