CSIT-220: Rename directories in tests directory

- Move performance directory one level up and rename it to “perf”
- Rename “suites” directory to “func”
- Create __init__.py in “perf” directory
- Rename fds_related_tests to fds

Change-Id: I59f06afe1c5b95dd8a48417b8fbfd1fca8797097
Signed-off-by: Matej Klotton <mklotton@cisco.com>