qa: add test for checking access in client side of root_squash

qa: add test for checking access in client side of root_squash

Test the 'chown' and 'truncate', which will call the setattr and
'cat' will open the files. Before each testing will open the file
by non-root user and keep it to make sure the Fxw caps are issued,
and then user the 'sudo' do to the tests, which will set the uid/gid
to 0/0.

Fixes: https://tracker.ceph.com/issues/57154
Signed-off-by: Xiubo Li <xiubli@redhat.com>