t: move reftable/basics_test.c to the unit testing framework

t: move reftable/basics_test.c to the unit testing framework

reftable/basics_test.c exercise the functions defined in
reftable/basics.{c, h}. Migrate reftable/basics_test.c to the
unit testing framework. Migration involves refactoring the tests
to use the unit testing framework instead of reftable's test
framework.

Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Chandra Pratap <chandrapratap3519@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>