pytest: Create xml coverage report for codecov (linux-system-roles#109)

Create the XML coverage report since this is the one that is needed for
codecov.

Note: codecov uses some heuristics to find the coverage file and it does
not seem to be possible to specify which file to use. The
get_coverage.yml playbook is also wrongly identified as a coverage
report which can be confusing if the actual report is not identified as
one.

Signed-off-by: Till Maas <opensource@till.name>
(cherry picked from commit ab14427)

src/tox_lsr/config_files/tox-default.ini

@@ -49,6 +49,7 @@ commands =
         python -m pytest -c {[lsr_pytest]configfile} --durations=5 \
         --cov={toxinidir}/library --cov={toxinidir}/module_utils \
         --cov-report=html:htmlcov-{envname} \
+        --cov-report=xml:coverage-{envname}.xml \
         --cov-report=term {env:RUN_PYTEST_EXTRA_ARGS:} {posargs} {env:RUN_PYTEST_UNIT_DIR:unit} ; \
         fi'
     {[lsr_config]commands_post}