Avoid warning in JUnit when using args that are not defined

[v1v]

What does this PR do?

Fix warning when using args that are not defined

[2020-10-13T16:50:43.188Z] [Pipeline] junit
[2020-10-13T16:50:43.188Z] WARNING: Unknown parameter(s) found for class type 'hudson.tasks.junit.pipeline.JUnitResultsStep': id,stashedTestReports
[2020-10-13T16:50:43.192Z] Recording test results
[2020-10-13T16:50:43.618Z] None of the test reports contained any result

Why is it important?

Let's see if that could be the reason with the BO issues and corrupted data.

Related issues

Relates to elastic/beats#21888

[ghost]

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Build stats

• Build Cause: [Pull request #775 opened]

• Start Time: 2020-10-16T11:41:04.971+0000

• Duration: 7 min 33 sec

Test stats 🧪

Test	Results
Failed	0
Passed	847
Skipped	9
Total	856