open_by_handle: test file handles of renamed files

open_by_handle: test file handles of renamed files

usage: open_by_handle -m <test_dir> [N]

Get file handles for existing test set, rename all test files,
drop cache and try to open all files by handle.

This is needed for testing that overlayfs can find the upper
inode from lower file handle even when upper is not in the same
path as lower.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>