net.box: fix box.error() usage

box.error() expects first argument to be numeric or table; passing
string to it is wrong. Accidentally in net.box module two places where
string is passed to box.error() as first argument: in :unprepare() and
:connect() methods. Let's fix them and pass error code ER_ILLEGAL_PARAMS.

NO_DOC=<bugfix>
NO_CHANGELOG=<Minor>

(cherry picked from commit a74c549a)

src/box/lua/net_box.lua

@@ -355,7 +355,8 @@ local function new_sm(uri, opts)
         end
     end
     if opts.console then
-        box.error("Netbox text protocol support was dropped, " ..
+        box.error(box.error.ILLEGAL_PARAMS,
+                  "Netbox text protocol support was dropped, " ..
                   "please use require('console').connect() instead")
     else
         setmetatable(remote, remote_mt)
@@ -817,7 +818,8 @@ end
 function remote_methods:unprepare(query, parameters, sql_opts, netbox_opts)
     check_remote_arg(self, "unprepare")
     if type(query) ~= "number" then
-        box.error("query id is expected to be numeric")
+        box.error(box.error.ILLEGAL_PARAMS,
+                  "query id is expected to be numeric")
     end
     if sql_opts ~= nil then
         box.error(box.error.UNSUPPORTED, "unprepare", "options")

test/box-luatest/net_box_test.lua

@@ -301,3 +301,16 @@ g.after_test('test_schemaless', function()
         end
     end)
 end)
+
+g.test_box_error = function()
+    t.assert_error_msg_equals(
+        "Illegal parameters, Netbox text protocol support was dropped, "..
+        "please use require('console').connect() instead",
+        net.connect, g.server.net_box_uri, {console = 123})
+    local c = net.connect(g.server.net_box_uri)
+
+    t.assert_error_msg_equals(
+        "Illegal parameters, query id is expected to be numeric",
+        c.unprepare, c, "asd")
+    c:close()
+end