testsuite: test that flux run --taskmap=block:foo fails

Problem: None of the shell taskmap tests ensure that an argument
specified with the block scheme is rejected by the shell.

Add a test to t2616-job-shell-taskmap.t.

Author: grondo

t/t2616-job-shell-taskmap.t

@@ -84,6 +84,10 @@ test_expect_success 'taskmap is unchanged with --taskmap=block' '
 		| jq -e ".context.taskmap.map == [[0,4,4,1]]" &&
 	test_check_taskmap $id
 '
+test_expect_success 'shell dies with --taskmap=block:oops' '
+	test_must_fail_or_be_terminated flux run -N4 --tasks-per-node=4 \
+		--taskmap=block:oops ./map.sh
+'
 test_expect_success 'taskmap is correct for --tasks-per-node=2' '
 	id=$(flux submit -N4 --tasks-per-node=2 ./map.sh) &&
 	flux job wait-event -p guest.exec.eventlog -f json $id shell.start &&