testsuite: cover response trace

Problem: there is no test coverage for flux module trace and
flux overlay trace's special handling of response messages.

Add a test for a failing RPC with human-readable error.

t/t3400-overlay-trace.t

@@ -43,6 +43,16 @@ test_expect_success NO_CHAIN_LINT 'kvs.ping request/response was captured' '
 test_expect_success NO_CHAIN_LINT 'kvs.ping request/response was captured with --full' '
 	$waitfile -t 60 -c 2 -p kvs.ping trace2.out
 '
+# This RPC happens to return a human readable error on failure
+test_expect_success NO_CHAIN_LINT 'send one job-manager.kill (failing)' '
+	test_must_fail flux exec -r 1 flux job kill fuzzybunny
+'
+test_expect_success NO_CHAIN_LINT 'job-manager.kill request/response was captured' '
+	$waitfile -t 60 -c 2 -p "job%-manager.kill" trace.out
+'
+test_expect_success NO_CHAIN_LINT 'job-manager.kill request/response was captured with --full' '
+	$waitfile -t 60 -c 2 -p "job%-manager.kill" trace2.out
+'
 test_expect_success NO_CHAIN_LINT 'stop background trace' '
 	pid=$(cat trace.pid) &&
 	kill -15 $pid &&

t/t3401-module-trace.t

@@ -21,11 +21,11 @@ test_expect_success 'reload heartbeat with increased heart rate' '
 	flux module reload heartbeat period=0.2s
 '
 test_expect_success NO_CHAIN_LINT 'start background trace' '
-	flux module trace kvs >trace.out &
+	flux module trace kvs job-manager >trace.out &
 	echo $! >trace.pid
 '
 test_expect_success NO_CHAIN_LINT 'start second background trace with --full' '
-	flux module trace --full kvs >trace1a.out &
+	flux module trace --full kvs job-manager >trace1a.out &
 	echo $! >trace1a.pid
 '
 test_expect_success NO_CHAIN_LINT 'heartbeat.pulse event was captured' '
@@ -43,6 +43,17 @@ test_expect_success NO_CHAIN_LINT 'kvs.ping request/response was captured' '
 test_expect_success NO_CHAIN_LINT 'kvs.ping request/response was captured with --full' '
 	$waitfile -t 60 -c 2 -p kvs.ping trace1a.out
 '
+# This RPC happens to return a human readable error on failure
+test_expect_success NO_CHAIN_LINT 'send one job-manager.kill (failing)' '
+	test_must_fail flux job kill fuzzybunny
+'
+test_expect_success NO_CHAIN_LINT 'job-manager.kill request/response was captured' '
+	$waitfile -t 60 -c 2 -p "job%-manager.kill" trace.out
+'
+test_expect_success NO_CHAIN_LINT 'job-manager.kill request/response was captured with --full' '
+	$waitfile -t 60 -c 2 -p "job%-manager.kill" trace1a.out
+'
+
 test_expect_success NO_CHAIN_LINT 'stop background trace' '
 	pid=$(cat trace.pid) &&
 	kill -15 $pid &&