[Edit Tail Fast Path Pt 4] Cleanup: integration test, documentation, remove unnecessary dummy sync

See HDFS-13150 for full design.

This JIRA is targeted at cleanup tasks:

• Add in integration testing. We can expand TestStandbyInProgressTail
• Documentation in HDFSHighAvailabilityWithQJM
• Remove the dummy sync added as part of HDFS-10519; it is unnecessary since now in-progress tailing does not rely on the JN committedTxnId

A few bugs are also fixed:

• Due to changes in HDFS-13609 to enable use of the RPC mechanism whenever inProgressOK is true, there were codepaths which would use the RPC mechanism even when dfs.ha.tail-edits.in-progress was false, meaning that the JNs did not enable the cache. Update the QJM logic to only use selectRpcInputStreams if this config is true.
• Fix a false error logged when the layout version changes
• Fix the logging when a layout version change occurs to avoid printing out a placeholder value (Integer.MAX_VALUE)