SegmentStats yaml test fails in mixed-cluster BWC

[polyfractal]

Looks like it started failing after the backport version change:

Seems to be failing pretty consistently so I'm going to mute the test.

 ./gradlew :qa:mixed-cluster:v7.1.0#mixedClusterTestRunner -Dtests.seed=D6DF7185080F7FEE -Dtests.class=org.elasticsearch.backwards.MixedClusterClientYamlTestSuiteIT -Dtests.method="test {p0=indices.stats/30_segments/Segment Stats}" -Dtests.security.manager=true -Dtests.locale=el-CY -Dtests.timezone=America/Halifax -Dcompiler.java=11 -Druntime.java=8

[2019-03-21T15:32:20,409][INFO ][o.e.b.MixedClusterClientYamlTestSuiteIT] [test] [p0=indices.stats/30_segments/Segment Stats] before test
14:34:45   1> [2019-03-21T15:32:20,625][INFO ][o.e.b.MixedClusterClientYamlTestSuiteIT] [test] Stash dump on test failure [{
14:34:45   1>   "stash" : {
14:34:45   1>     "num_segments_after_flush" : 1,
14:34:45   1>     "body" : {
14:34:45   1>       "_shards" : {
14:34:45   1>         "total" : 1,
14:34:45   1>         "successful" : 0,
14:34:45   1>         "failed" : 0
14:34:45   1>       },
14:34:45   1>       "_all" : {
14:34:45   1>         "primaries" : { },
14:34:45   1>         "total" : { }
14:34:45   1>       },
14:34:45   1>       "indices" : { }
14:34:45   1>     },
14:34:45   1>     "num_segments" : 0
14:34:45   1>   }
14:34:45   1> }]
14:34:45   1> [2019-03-21T15:32:20,681][INFO ][o.e.b.MixedClusterClientYamlTestSuiteIT] [test] [p0=indices.stats/30_segments/Segment Stats] after test
14:34:45 FAILURE 0.28s | MixedClusterClientYamlTestSuiteIT.test {p0=indices.stats/30_segments/Segment Stats} <<< FAILURES!
14:34:45    > Throwable #1: java.lang.AssertionError: Failure at [indices.stats/30_segments:53]: field [indices.test.primaries.segments.count] is null
14:34:45    > 	at __randomizedtesting.SeedInfo.seed([D6DF7185080F7FEE:5E8B4E5FA6F31216]:0)
14:34:45    > 	at org.elasticsearch.test.rest.yaml.ESClientYamlSuiteTestCase.executeSection(ESClientYamlSuiteTestCase.java:393)
14:34:45    > 	at org.elasticsearch.test.rest.yaml.ESClientYamlSuiteTestCase.test(ESClientYamlSuiteTestCase.java:370)
14:34:45    > 	at java.lang.Thread.run(Thread.java:748)
14:34:45    > Caused by: java.lang.AssertionError: field [indices.test.primaries.segments.count] is null
14:34:45    > 	at org.elasticsearch.test.rest.yaml.section.MatchAssertion.doAssert(MatchAssertion.java:79)
14:34:45    > 	at org.elasticsearch.test.rest.yaml.section.Assertion.execute(Assertion.java:76)
14:34:45    > 	at org.elasticsearch.test.rest.yaml.ESClientYamlSuiteTestCase.executeSection(ESClientYamlSuiteTestCase.java:386)
14:34:45    > 	... 37 more

[elasticmachine]

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