[CI] LogStructureFinderManagerTests#testFindCharsetGivenBinary fails reproducibly

[cbuescher]

Build: https://elasticsearch-ci.elastic.co/job/elastic+elasticsearch+6.x+periodic/2636/console

I can reproduce locally on 6.x with:

./gradlew :x-pack:plugin:ml:log-structure-finder:test \
  -Dtests.seed=BB9C1AA2C3B090DF \
  -Dtests.class=org.elasticsearch.xpack.ml.logstructurefinder.LogStructureFinderManagerTests \
  -Dtests.method="testFindCharsetGivenBinary" \
  -Dtests.security.manager=true \
  -Dtests.locale=id \
  -Dtests.timezone=America/Punta_Arenas \
  -Dcompiler.java=10 \
  -Druntime.java=8

Error:

ERROR   0.31s | LogStructureFinderManagerTests.testFindCharsetGivenBinary <<< FAILURES!
   > Throwable #1: java.lang.UnsupportedOperationException
   >    at __randomizedtesting.SeedInfo.seed([BB9C1AA2C3B090DF:4A943652575C61C1]:0)
   >    at sun.nio.cs.ext.ISO2022_CN.newEncoder(ISO2022_CN.java:76)
   >    at java.lang.StringCoding$StringEncoder.<init>(StringCoding.java:282)
   >    at java.lang.StringCoding$StringEncoder.<init>(StringCoding.java:273)
   >    at java.lang.StringCoding.encode(StringCoding.java:338)
   >    at java.lang.String.getBytes(String.java:918)
   >    at org.elasticsearch.xpack.ml.logstructurefinder.LogStructureFinderManager.findCharset(LogStructureFinderManager.java:166)
   >    at org.elasticsearch.xpack.ml.logstructurefinder.LogStructureFinderManagerTests.testFindCharsetGivenBinary(LogStructureFinderManagerTests.java:42)
   >    at java.lang.Thread.run(Thread.java:748)

[elasticmachine]

Pinging @elastic/ml-core