JUnit writes local-time without a timezone by default.  This means that
JUnit XML parsers default to local-time.  The portal doesn't know what
timezone the user of stbt-rig wants so these timestamps can be interpreted
incorrectly.  This change includes timezone information in the XML output.

There is a small chance of incompatibilty caused by this change.  If you
experience this please get in contact at support@stb-tester.com.

…8.04

To fix "AttributeError: module 'isort' has no attribute 'SortImports'".

See
https://docs.pytest.org/en/stable/deprecations.html#node-construction-changed-to-node-from-parent

Errors were:

```
************* Module stbt_rig
stbt_rig.py:1237:4: [W0223(abstract-method), StbtCollector] Method 'get_closest_marker' is abstract in class 'Node' but is not overridden
stbt_rig.py:1237:4: [W0223(abstract-method), StbtCollector] Method 'gethookproxy' is abstract in class 'FSCollector' but is not overridden
stbt_rig.py:1237:4: [W0223(abstract-method), StbtCollector] Method 'isinitpath' is abstract in class 'FSCollector' but is not overridden
stbt_rig.py:1257:4: [W0223(abstract-method), StbtRemoteTest] Method 'get_closest_marker' is abstract in class 'Node' but is not overridden
```

The `get_closest_marker` is a pylint false positive because it's defined
multiple times in `class Node`:

```python
class Node(metaclass=NodeMeta):
    ...
    @overload
    def get_closest_marker(self, name: str) -> Optional[Mark]:
        raise NotImplementedError()

    @overload  # noqa: F811
    def get_closest_marker(self, name: str, default: Mark) -> Mark:  # noqa: F811
        raise NotImplementedError()

    def get_closest_marker(  # noqa: F811
        self, name: str, default: Optional[Mark] = None
    ) -> Optional[Mark]:
        """return the first marker matching the name, from closest (for example function) to farther level (for example
        module level).

        :param default: fallback return value of no marker was found
        :param name: name to filter by
        """
        return next(self.iter_markers(name=name), default)
```

The other two don't need to be inherited because they'll never be called:
pytest-dev/pytest#7591 .  This is fixed in
pytest 6.1: pytest-dev/pytest#7648