NFS weirdnesses handling
Try to handle NFS shortcomings that show up especially when the ping is executed very frequently on a multi-container environment, in parallel. The main problems are:
- Filesystem test tiles show up much later after the creation, so immediate file operations on that file would fail.
- Mtime on those test files is random, usually much less than a current timestamp. This prevents ping to understand if the file is a leftover from some earlier execution or from a running parallel ping.