tests: add tests for basename's --zero option

tests: add tests for basename's --zero option

The -z option has been introduced in commit v8.15-60-ga3eb71a,
i.e. in coreutils-8.16.  Time to add some tests for it.

* tests/misc/basename.pl: Add tests exercising the -z option.
In the foreach loop to append a newline to the end of each
expected 'OUT' string, skip the -z tests.