junitxml: Fix double system-out tags per testcase

[KKoukiou]

In the xml report we now have two occurrences for the system-out tag if
the testcase writes to stdout both on call and teardown and fails in
teardown.
This behaviour is against the xsd.
This patch makes sure that the system-out section exists only once per testcase.

How to reproduce:

@pytest.fixture(scope="function")
def setup_test(request):
    print("I am in setup")
    yield
    print("I am in teardown")
    raise Exception("test teardown Exception!")
    
def test_1(setup_test):
    print("I am in call")

Gives output:

<?xml version="1.0" encoding="utf-8"?>
<testsuite errors="1" failures="0" name="pytest" skips="0" tests="2" time="0.017">
  <testcase classname="test.test2" file="test/test2.py" line="11" name="test_1" time="0.000563859939575">
    <system-out>
    I am in setup
    I am in call
    </system-out>
    <error message="test teardown failure">request = &lt;SubRequest 'setup_test' for &lt;Function 'test_1'&gt;&gt;

    @pytest.fixture(scope="function")
    def setup_test(request):
        print("I am in setup")
        yield
        print("I am in teardown")
&gt;       raise Exception("test teardown Exception!")
E       Exception: test teardown Exception!

../../test/test2.py:9: Exception
    </error>
    <system-out>
    I am in setup
    I am in call
    I am in teardown
    </system-out>
  </testcase>
</testsuite>

Notice int he above output the double occurrence of the system-out tag.

[KKoukiou]

The reason I noticed this problem is the following: we use Jenkins Junit plugin to parse the xml file and show the TestReport in Jenkins. The former when it encounters two system-out tags in a testcase element, it accepts the first and discards the second tag. As a result we lose the stdout prints from teardown.

[coveralls]

Coverage decreased (-0.0008%) to 92.708% when pulling 3a70140 on KKoukiou:double-tag into 6680cb9 on pytest-dev:master.

[coveralls]

Coverage decreased (-0.0008%) to 92.708% when pulling d3a6be4 on KKoukiou:double-tag into 6680cb9 on pytest-dev:master.

[coveralls]

Coverage decreased (-0.0008%) to 92.708% when pulling d3a6be4 on KKoukiou:double-tag into 6680cb9 on pytest-dev:master.

[coveralls]

Coverage decreased (-0.0008%) to 92.708% when pulling d3a6be4 on KKoukiou:double-tag into 6680cb9 on pytest-dev:master.