logd: liblog benchmark check BM_log_overhead regression

Failed to acquire BM_log_print_overhead as it was renamed from
BM_log_overhead in commit 8f2492f5
(liblog: benchmark: Use local LOGGER_NULL frontend')

The test report would not clearly identify which entry was missing, or
unparsed, so unrolled the loop and incorporating the indexes by name
so that gTest failure report offers a much better clue to the problem.

Test: gTest logd-unit-tests --gtest=logd.benchmark
Bug: 36683634
Bug: 27405083
Change-Id: Ic590c230569871651fb716054ecf635385d0f8a2