Changed message for Model.inspect

(No database connection) sounds not be
able to connect database.

see more #12804

activerecord/lib/active_record/core.rb

@@ -109,7 +109,7 @@ module ActiveRecord
         elsif abstract_class?
           "#{super}(abstract)"
         elsif !connected?
-          "#{super}(no database connection)"
+          "#{super} (call '#{super}.connection' to establish a connection)"
         elsif table_exists?
           attr_list = columns.map { |c| "#{c.name}: #{c.type}" } * ', '
           "#{super}(#{attr_list})"

activerecord/test/cases/invalid_connection_test.rb

@@ -17,6 +17,6 @@ class TestAdapterWithInvalidConnection < ActiveRecord::TestCase
   end
 
   test "inspect on Model class does not raise" do
-    assert_equal "#{Bird.name}(no database connection)", Bird.inspect
+    assert_equal "#{Bird.name} (call '#{Bird.name}.connection' to establish a connection)", Bird.inspect
   end
 end