broker: check type of [queues] table

Problem: a malformed queues config such as queues=42 is
allowed by the broker policy/queues config validator.

Check that queues is a table.
Add test to t2241-policy-config.t.

Drop t2112-job-ingest-frobnicator.t test that expects that to get
through the broker and fail in the frobnicator.

src/broker/brokercfg.c

@@ -289,6 +289,10 @@ static int validate_queues_config (flux_conf_t *conf, flux_error_t *error)
         const char *name;
         json_t *entry;
 
+        if (!json_is_object (queues)) {
+            errprintf (error, "queues must be a table");
+            goto inval;
+        }
         json_object_foreach (queues, name, entry) {
             json_error_t jerror;
             json_t *policy = NULL;

t/t2112-job-ingest-frobnicator.t

@@ -107,19 +107,6 @@ test_expect_success 'job-frobnicator errors on a missing queue config' '
 	       >bad1.out 2>&1 &&
 	grep "default queue.*debug.*must be in" bad1.out
 '
-test_expect_success 'job-frobnicator errors on an invalid queue config' '
-	cat <<-EOF >conf.d/conf.toml &&
-	queues = 42
-	[policy.jobspec.defaults.system]
-	queue = "debug"
-	EOF
-	flux config reload &&
-	flux mini run --env=-* --dry-run hostname \
-	   | test_expect_code 1 \
-	       flux job-frobnicator --jobspec-only --plugins=defaults \
-	       >bad2.out 2>&1 &&
-	grep "queues must be a table" bad2.out
-'
 test_expect_success 'configure queue constraints' '
 	cat <<-EOF >conf.d/conf.toml &&
 	[queues.debug]

t/t2241-policy-config.t

@@ -124,6 +124,12 @@ test_expect_success 'well formed policy.access works' '
 	EOT
 	flux config reload
 '
+test_expect_success 'malformed queues table fails' '
+	cat >config/policy.toml <<-EOT &&
+	queues = 1
+	EOT
+	test_must_fail flux config reload
+'
 test_expect_success 'unknown queues.NAME.policy.foo key fails' '
 	cat >config/policy.toml <<-EOT &&
 	queues.x.policy.foo = 1