testsuite: fix test_array_sort pointers inderection

testsuite: fix test_array_sort pointers inderection

The array elements in the tests are strings, what means "char *"
in С. The comparation funtion takes pointers to the elements, so
the arguments become "char **". It means, that strcmp() cannot be
used directrly.

The patch creates a wrapper on strcmp() which perfoms
dereferencing of the "char **" to supply the actual strings to
strcmp(), and uses the wrapper as a comparation function for the
qsort() call.

Signed-off-by: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>