TestJoinUtil.testSingleValueRandomJoin() failure [LUCENE-7571]

My Jenkins found a reproducing branch_6x seed:

```
Checking out Revision 500f6c7875be31c34ca68c58f850b7e64fd049a9 (refs/remotes/origin/branch_6x)
[...]
[junit4] Suite: org.apache.lucene.search.join.TestJoinUtil
[junit4] 2> NOTE: reproduce with: ant test -Dtestcase=TestJoinUtil -Dtests.method=testSingleValueRandomJoin -Dtests.seed=D50603847B355BCB -Dtests.slow=true -Dtests.locale=sq -Dtests.timezone=America/Indianapolis -Dtests.asserts=true -Dtests.file.encoding=US-ASCII
[junit4] FAILURE 1.42s J0 | TestJoinUtil.testSingleValueRandomJoin <<<
[junit4] > Throwable #1: java.lang.AssertionError: expected: but was:
[junit4] > at __randomizedtesting.SeedInfo.seed([D50603847B355BCB:39BE12CEF3F64714]:0)
[junit4] > at org.apache.lucene.search.join.TestJoinUtil.assertBitSet(TestJoinUtil.java:1046)
[junit4] > at org.apache.lucene.search.join.TestJoinUtil.executeRandomJoin(TestJoinUtil.java:1023)
[junit4] > at org.apache.lucene.search.join.TestJoinUtil.testSingleValueRandomJoin(TestJoinUtil.java:938)
[junit4] > at java.lang.Thread.run(Thread.java:745)
[junit4] 2> NOTE: test params are: codec=Asserting(Lucene62), sim=RandomSimilarity(queryNorm=false,coord=yes): {productId=ClassicSimilarity, field=DFR I(F)2, price=DFR GB1, subtitle=DFR I(n)L3(800.0), name=DFR G1, description=DFR GL2, from=DFR GB2, movieId=IB LL-L2, id=DFR I(ne)L1, to=DFR I(ne)BZ(0.3), type=DFR I(n)L2, value=DFR I(ne)2}, locale=sq, timezone=America/Indianapolis
[junit4] 2> NOTE: Linux 4.1.0-custom2-amd64 amd64/Oracle Corporation 1.8.0_77 (64-bit)/cpus=16,threads=1,free=495200800,total=522715136
[junit4] 2> NOTE: All tests run in this JVM: [TestJoinUtil]
[junit4] Completed [5/6 (1!)] on J0 in 9.20s, 13 tests, 1 failure <<< FAILURES!
```

---
Migrated from [LUCENE-7571](https://issues.apache.org/jira/browse/LUCENE-7571) by Steven Rowe (@sarowe), updated Jun 19 2017