Introduce Broken Strategy State, Prevent Further Use and Skip Subsequent Tests

[Bastian-Krause]

Description
Introduce a decorator for the Strategy's transition() and force() methods. It stores the original exception in the Strategy's new broken attribute and raises a StrategyError from it. All subsequent calls to the decorated method will lead to the original exception.

Now that a Strategy can be marked broken easily, check for that in labgrid's pytest plugin before executing a test and its fixtures. If a broken Strategy is found in one of the targets, skip the test. It's not worth continuing with it. It only leads to cascading and confusing errors.

Having a strategy prepared with the new decorator, a strategy exception now leads to either a test error (when triggered in a fixture) or a test fail (when triggered in the test itself). All subsequent tests requesting the broken strategy (via the strategy fixture) will be skipped.

In order to get the word out about the @raise_if_broken decorator, decorate the Strategies in labgrid with it.

Previously this kind of workaround was often used:

@pytest.fixture
def shell(strategy, target):
    try:
        strategy.transition("shell")
        return target.get_driver("ShellDriver")
    except Exception:
        pytest.exit("Strategy failed")

This is now obsolete.

Checklist

• Documentation for the feature
• Tests for the feature (covered in tests/test_docker.py::test_docker_without_daemon)
• Add a section on how to use the feature to doc/usage.rst
• Add a section on how to use the feature to doc/development.rst
• PR has been tested

Related to #1123.

[codecov]

Codecov Report

Attention: Patch coverage is 80.55556% with 7 lines in your changes missing coverage. Please review.

Project coverage is 55.7%. Comparing base (e43d093) to head (0815740).
Report is 9 commits behind head on master.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
labgrid/pytestplugin/hooks.py	40.0%	6 Missing ⚠️
labgrid/strategy/common.py	92.3%	1 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff           @@
##           master   #1681   +/-   ##
======================================
  Coverage    55.6%   55.7%           
======================================
  Files         172     172           
  Lines       13466   13501   +35     
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+ Hits         7492    7523   +31     
- Misses       5974    5978    +4     

Flag	Coverage Δ
3.10	55.7% <80.5%> (+<0.1%)	⬆️
3.11	55.7% <80.5%> (+<0.1%)	⬆️
3.12	55.7% <80.5%> (+<0.1%)	⬆️
3.13	55.6% <80.5%> (+<0.1%)	⬆️
3.9	55.7% <80.5%> (+<0.1%)	⬆️

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