testsuite: add check for proctable service security

Add test to ensure proctable shell service is not accessible to
all users in t2610-job-shell-mpir.t.

t/t2610-job-shell-mpir.t

@@ -34,4 +34,21 @@ for test in 1:1 2:2 2:4 4:4 4:8 4:7; do
         flux job attach ${id}
     '
 done
+
+
+test_expect_success 'flux-shell: test security of proctable method' '
+    id=$(flux mini submit -o stop-tasks-in-exec /bin/true) &&
+    flux job wait-event -vt 5 -p guest.exec.eventlog \
+        -m sync=true ${id} shell.start &&
+    shell_rank=$(shell_leader_rank $id) &&
+    shell_service=$(shell_service $id) &&
+    ( export FLUX_HANDLE_USERID=9999 &&
+      export FLUX_HANDLE_ROLEMASK=0x2 &&
+      test_expect_code 1 ${mpir} $shell_rank $shell_service
+    ) &&
+    ${mpir} $(shell_leader_rank $id) $(shell_service $id) &&
+    flux job kill -s CONT ${id} &&
+    flux job attach ${id}
+'
+
 test_done