Fixed test failure for JEChangeNumberIndexDBTest.testClear().
Problem was due to the CNIndexDB state not being properly cleaned up.
I chose to rely on ReplicationTestCase.remove(ReplicationServer) to clean up the state of the ChangeNumberIndexDB.


JEChangelogDB.java:
Extracted getChangeNumberIndexDB(boolean) from getChangeNumberIndexDB().

JEChangeNumberIndexDB.java:
Removed trimDone field.
In shutdown(), used Thread.join().
In run(), removed duplicated code that I unfortunately added there in r9881.

JEChangeNumberIndexDBTest.java:
Replaced newCNIndexDB() with getCNIndexDBNoTrimming() + Removed createCleanDir() + relied on ReplicationTestCase.remove(ReplicationServer) to clean up the state of the ChangeNumberIndexDB.