[CI] TermsAggregatorTests.testManyUniqueTerms failure

[matriv]

Build scan:
https://gradle-enterprise.elastic.co/s/zs7wpexyuupcg

Repro line:

./gradlew ':server:test' --tests "org.elasticsearch.search.aggregations.bucket.terms.TermsAggregatorTests.testManyUniqueTerms" \
  -Dtests.seed=928BECEE0B850D70 \
  -Dtests.security.manager=true \
  -Dtests.locale=ar-SD \
  -Dtests.timezone=America/Indiana/Knox \
  -Druntime.java=8

Reproduces locally?:
YES

Applicable branches:
7.12

Failure history:
https://build-stats.elastic.co/app/kibana#/discover?_g=(refreshInterval:(pause:!t,value:0),time:(from:now-90d,mode:quick,to:now))&_a=(columns:!(_source),index:e58bf320-7efd-11e8-bf69-63c8ef516157,interval:auto,query:(language:lucene,query:testManyUniqueTerms),sort:!(time,desc))

Failure excerpt:

10:46:22   2> java.lang.AssertionError: 
10:46:22     Expected: <[b007, b107, b207, b307, b407, b507, b607, b707, b000, b001]>
10:46:22          but: was <[b007, b107, b207, b307, b407, b507, b707, b000, b001, b002]>
10:46:22         at __randomizedtesting.SeedInfo.seed([928BECEE0B850D70:E65ADE16B0EDEB46]:0)
10:46:22         at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:18)
10:46:22         at org.junit.Assert.assertThat(Assert.java:956)
10:46:22         at org.junit.Assert.assertThat(Assert.java:923)
10:46:22         at org.elasticsearch.search.aggregations.bucket.terms.TermsAggregatorTests.lambda$testManyUniqueTerms$6(TermsAggregatorTests.java:304)
10:46:22         at org.elasticsearch.search.aggregations.AggregatorTestCase.testCase(AggregatorTestCase.java:545)
10:46:22         at org.elasticsearch.search.aggregations.bucket.terms.TermsAggregatorTests.testManyUniqueTerms(TermsAggregatorTests.java:295)

[elasticmachine]

Pinging @elastic/es-analytics-geo (Team:Analytics)

[nik9000]

Thanks for filing this! It's certainly my bug. I'll work on a fix this afternoon.