tests: fix an ls test not to fail when user or group name contains SP

tests: fix an ls test not to fail when user or group name contains SP

* tests/ls/block-size.sh (size_etc): The sed expression through which
we filtered the output of "ls -l ..." assumed that the user and group
name components of each line would not contain spaces.  Avoid the
problem by using -og instead of -l, thus not printing either of those
fields.  Adjust the sed expression accordingly.