This commit handles the scenario where a replication action fails on a
replica shard, the primary shard attempts to fail the replica shard
but the primary shard is notified of demotion by the master. In this
scenario, the demoted primary shard must be failed, and then the
request rerouted again to the new primary shard.

This commit removes a logging statement from TransportReplicationAction
that occurs when handling a catastrophic non-channel failure while
failing a shard. The same information is also logged from
ShardStateAction when the master responds to the shard failure request
there.

This commit significantly simplifies the retry logic upon a demoted
primary shard. In particular, rather failing the demoted primary via
shard state action and starting a new reroute phase, this commit
simplifies this logic by failing the demoted primary via an index shard
reference, and sending a retry on primary exception back to the original
reroute phase.

This commit adds a dedicated test for handling the situation of a
demoted primary shard that was trying to fail a replica shard during a
replication action.

This commit removes a dead request parameter from the constructor of
TransportReplicationAction.ReplicationPhase.

* master: (85 commits)
  Rename variables.
  BootstrapSettings final with private constructor
  simplify method signature
  Register bootstrap settings
  Fix asciidoc typo
  Log warning if max file descriptors too low
  Require that relocation source is marked as relocating before starting recovery to relocation target
  apply feedback from @colings86
  Speedup MessageDigestTests#testToHexString
  Fix serialization of `search_analyzer`.
  Cleanup JavaVersion
  Detach QueryShardContext from IndexShard and remove obsolete threadlocals
  Move sorting tests w/o scripting back to core
  Fix recovery translog stats totals when recovering from store
  [TEST] Don't assert on null value. It's fine to not always see an exception in this part of the test.
  Objects#requireNonNull guard in MessageDigests
  Fix trace logging statement in ZenDiscovery
  Avoid cloning MessageDigest instances
  Minor clean up.
  Make IndicesWarmer a private class of IndexService
  ...