generic: add test with more open by file handle use cases

generic: add test with more open by file handle use cases

This test is a variant of test generic/426 that tests with less
files and more use cases:
- Create test dir with non empty files with known content and verify
  their content after opening file by handle.
- Check open by handle of directory.
- Check open by handle of files that have been unlinked, but still open.
- Check open by handle of files that have been renamed in same dir,
  moved to new dir and whose parent dir has been renamed.

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