tests: Ship elm_test_helper.h in dist tarball
tests: Ship elm_test_helper.h in dist tarball

This is a first step to run elm make check during distcheck.

tasn/elementary,FlorentRevest/Elementary,FlorentRevest/Elementary,FlorentRevest/Elementary,rvandegrift/elementary,FlorentRevest/Elementary,tasn/elementary,rvandegrift/elementary,rvandegrift/elementary,tasn/elementary,tasn/elementary,tasn/elementary,rvandegrift/elementary