Make our C test main report APR error in more detail.

* subversion/tests/svn_test_main.c
  (CHECK_STATUS): New utility macro.
  (do_tests_concurrently): Use the new macro get nice(r)
                           reporting for APR errors.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1546445 13f79535-47bb-0310-9956-ffa450edef68