Add an ability to use assert_items_include with tuples

[palage4a]

local t = require('luatest')
local g = t.group()

local a = {1,2,3}
local b = box.tuple.new(a)
local c = box.tuple.new(a)

-- unable to assert table with tuple
g.test_table_includes_tuple = function()
    t.assert_items_include(a, b)
end
-- even unable to assert tuple with tuple
g.test_tuple_includes_tuple = function()
    t.assert_items_include(b, c)
end

$ .rocks/bin/luatest ./test
Tarantool version is 2.11.0-0-gc9673ebb7-r575-gc64
FF

Failed tests:
-------------

1) tuples_assert.test_table_includes_tuple
...ge4a/tmp/assert-tuples/app///test/tuples_assert_test.lua:10: Expected all item values from: [1, 2, 3]
To be present in: {1, 2, 3}
stack traceback:
	...ge4a/tmp/assert-tuples/app///test/tuples_assert_test.lua:10: in function 'tuples_assert.test_table_includes_tuple'
	...
	[C]: in function 'xpcall'
2) tuples_assert.test_tuple_includes_tuple
...ge4a/tmp/assert-tuples/app///test/tuples_assert_test.lua:14: Expected all item values from: [1, 2, 3]
To be present in: [1, 2, 3]
stack traceback:
	...ge4a/tmp/assert-tuples/app///test/tuples_assert_test.lua:14: in function 'tuples_assert.test_tuple_includes_tuple'
	...
	[C]: in function 'xpcall'
Ran 2 tests in 0.001 seconds, 0 succeeded, 2 failed

Failed tests:

tuples_assert.test_table_includes_tuple
tuples_assert.test_tuple_includes_tuple