open_by_handle: add support for testing connectable file handles

open_by_handle: add support for testing connectable file handles

Test for kernel and filesystem support for conenctable file handles.

With -N flag, encode connectable file handles and fail the test if the
kernel or filesystem do not support conenctable file handles.

Verify that decoding connectable file handles always results in a non
empty path of the fd.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>