The `enable-scripting` parameter allows to specify a LibreOffice script
to be applied before saving the document, as per
nexedi/cloudooo@a09d87af
If false (the default), an exception will be raised instead.

This commit also adds two SlapOS integration tests classes to test the
functionality:
- TestScripting requests an instance with scripting enabled, and tests
the scripting functionality.
- TestScriptingDisabled tests that scripting fails if it is not enabled
explicitly.