DateMathIndexExpressionsIntegrationIT#testIndexNameDateMathExpressions() fails in CI

[danielmitterdorfer]

CI link: https://elasticsearch-ci.elastic.co/job/elastic+elasticsearch+master+multijob-unix-compatibility/os=centos/2477/console

Failure:

11:46:07 FAILURE 0.50s J1 | DateMathIndexExpressionsIntegrationIT.testIndexNameDateMathExpressions <<< FAILURES!
11:46:07    > Throwable #1: java.lang.AssertionError: 
11:46:07    > Expected: not null
11:46:07    >      but: was null
11:46:07    > 	at __randomizedtesting.SeedInfo.seed([B7B9B064B801973A:3CDA461B4CC8D5A4]:0)
11:46:07    > 	at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:20)
11:46:07    > 	at org.elasticsearch.indices.DateMathIndexExpressionsIntegrationIT.testIndexNameDateMathExpressions(DateMathIndexExpressionsIntegrationIT.java:94)
11:46:07    > 	at java.lang.Thread.run(Thread.java:748)

(meaning that the indices stats API did not return an index with the name .marvel-2018.06.04).

reproduction line:

./gradlew :server:integTest \
  -Dtests.seed=B7B9B064B801973A \
  -Dtests.class=org.elasticsearch.indices.DateMathIndexExpressionsIntegrationIT \
  -Dtests.method="testIndexNameDateMathExpressions" \
  -Dtests.security.manager=true \
  -Dtests.locale=sr \
  -Dtests.timezone=Asia/Dushanbe

Does not reproduce locally. This failure has occurred four times within the last year in CI.

[elasticmachine]

Pinging @elastic/es-core-infra