Review and complete mountpoint test protocol

[mmmarcos]

Mountpoint test coverage needs to be improved.

We should start listing the current tests so we can complete them based on recent reported bugs (e.g. #8764, #8907, #8991).

Additionally, we should think about which parts of the mountpoint test protocol can be automated locally. For example, we could have a script that uses system utilities (cp, mv, rm, ...) to perform basic tests.