fix_core_name: update test/run_tests.sh to remove core

test/run_tests.sh

@@ -23,6 +23,10 @@ rc=0
 test_bins="test_butil test_bvar bthread*unittest brpc*unittest"
 ulimit -c unlimited # turn on coredumps
 for test_bin in $test_bins; do
+    # test_butil would generate core file due to ASSERT_DEATH and still be passed.
+    # The core file should be removed first otherwise other core would not be
+    # generated.
+    rm -rf core*
     test_num=$((test_num + 1))
     >&2 echo "[runtest] $test_bin"
     ./$test_bin