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##### SUMMARY
<!--- Explain the problem briefly below -->
`unique` filter does not respect the order and gives non-idempotent results

##### ISSUE TYPE
- Bug Report


##### COMPONENT NAME
lib/ansible/plugins/filter/mathstuff.py


##### ANSIBLE VERSION
<!--- Paste verbatim output from "ansible --version" between quotes -->
```paste below
ansible 2.8.5
```

##### STEPS TO REPRODUCE
<!--- Describe exactly how to reproduce the problem, using a minimal test-case -->
I have the following statement in my template 

```jinja2
{% for host in url_list | map('urlsplit', 'hostname') | unique %}
    upstream {{ host }} {
        server {{ host }}:443;
        keepalive 20;
        keepalive_requests 500;
        keepalive_timeout 30s;
    }
{% endfor %}
```

which basically extracts unique host names from some url list and declares upstream server for each. 

##### EXPECTED RESULTS
The order of hosts is at least consistent between runs. 


##### ACTUAL RESULTS
The order of hosts is different for each run. Unexpected handlers are triggered.

def test_unhashable(self, data, expected):
        assert sorted(ms.unique(env, list(data))) == expected
    def test_hashable(self, data, expected):
        assert sorted(ms.unique(env, tuple(data))) == expected
@pytest.mark.parametrize('dataset1, dataset2, expected', TWO_SETS_DATA)
class TestIntersect:
    def test_unhashable(self, dataset1, dataset2, expected):
        assert sorted(ms.intersect(env, list(dataset1), list(dataset2))) == expected[0]
    def test_hashable(self, dataset1, dataset2, expected):
        assert sorted(ms.intersect(env, tuple(dataset1), tuple(dataset2))) == expected[0]
@pytest.mark.parametrize('dataset1, dataset2, expected', TWO_SETS_DATA)
class TestDifference:
    def test_unhashable(self, dataset1, dataset2, expected):
        assert sorted(ms.difference(env, list(dataset1), list(dataset2))) == expected[1]
    def test_hashable(self, dataset1, dataset2, expected):
        assert sorted(ms.difference(env, tuple(dataset1), tuple(dataset2))) == expected[1]
@pytest.mark.parametrize('dataset1, dataset2, expected', TWO_SETS_DATA)
class TestSymmetricDifference:
    def test_unhashable(self, dataset1, dataset2, expected):
        assert sorted(ms.symmetric_difference(env, list(dataset1), list(dataset2))) == expected[2]
    def test_hashable(self, dataset1, dataset2, expected):
        assert sorted(ms.symmetric_difference(env, tuple(dataset1), tuple(dataset2))) == expected[2]
class TestMin: