Improved test suite for rmtree

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Related tickets | 
| License       | GNU GPL v3

- [x] Add a test for remove symbolic links to file and directory
- [x] Add a test for remove symbolic link that point to a previous deleted file