Print out multiple snabb instance pids

src/program/top/top.lua

@@ -39,14 +39,20 @@ function select_snabb_instance (pid)
          if instance == pid then return pid end
       end
       print("No such Snabb instance: "..pid)
-   elseif #instances == 2 then
-      -- Two means one is us, so we pick the other.
-      local own_pid = tostring(S.getpid())
-      if instances[1] == own_pid then return instances[2]
-      else                            return instances[1] end
    elseif #instances == 1 then print("No Snabb instance found.")
-   else print("Multple Snabb instances found. Select one.") end
-   os.exit(1)
+   else
+      local own_pid = tostring(S.getpid())
+      if #instances == 2 then
+         -- Two means one is us, so we pick the other.
+         return instances[1] == own_pid and instances[2] or instances[1]
+      else
+         print("Multiple Snabb instances found. Select one:")
+         for _, instance in ipairs(instances) do
+            if instance ~= own_pid then print(instance) end
+         end
+      end
+   end
+   main.exit(1)
 end
 
 function list_shm (pid, object)