[CI] Periodic matrix tests fail FIPS8 with :x-pack:plugin:security:cli:testingConventions

[cbuescher]

Looks like all of the recent failures are related to failing the :x-pack:plugin:security:cli:testingConventions task.

https://elasticsearch-ci.elastic.co/job/elastic+elasticsearch+6.x+matrix-java-periodic/ES_BUILD_JAVA=java11,ES_RUNTIME_JAVA=java8fips,nodes=immutable&&linux&&docker/

e.g. in this build:

https://elasticsearch-ci.elastic.co/job/elastic+elasticsearch+6.x+matrix-java-periodic/ES_BUILD_JAVA=java11,ES_RUNTIME_JAVA=java8fips,nodes=immutable&&linux&&docker/222/consoleFull

11:10:51 > Task :x-pack:plugin:security:cli:testingConventions FAILED
11:10:51 Test classes are not included in any enabled task ():
11:10:51 Build cache key for task ':x-pack:plugin:security:cli:testingConventions' is 11e64d8aa2514b12ec5f552dc1b56b17
11:10:51   * org.elasticsearch.xpack.security.cli.CertGenUtilsTests
11:10:51   * org.elasticsearch.xpack.security.cli.CertificateGenerateToolTests

[elasticmachine]

Pinging @elastic/es-security

[jkakavas]

This should be resolved in #38546