Rename torture test

[MorrisJobke]

• create a folder with many files in it (the more files the higher the propability will be that the problem occurs)
• sync that folder
• rename it -> will take long
• do a parallel request to the old folder (this will trigger to delete the entries, because the files aren't present on the filesystem but in the filecache -> drop of entry -> we lost also the file id -> we lost the linked shares) - the entries are dropped, because the update of the data in step 3 isn't finished

cc @jnweiger because you wrote a bash script in core: owncloud/core#14542