* WIP, basic implementation

* Pull `if` branch into a variable

* Remove outdated javadoc

* Remove map iteration, use target name instead of id (whoops)

* Remove streaming from isReplacementSource

* Simplify getReplacementName

* Only calculate node shutdowns if canRemain==false and forceMove==false

* Move canRebalance comment in BalancedShardsAllocator

* Rename canForceDuringVacate -> canForceAllocateDuringReplace

* Add comment to AwarenessAllocationDecider.canForceAllocateDuringReplace

* Revert changes to ClusterRebalanceAllocationDecider

* Change "no replacement" decision message in NodeReplacementAllocationDecider

* Only construct shutdown map once in isReplacementSource

* Make node shutdowns and target shutdowns available within RoutingAllocation

* Add randomization for adding the filter that is overridden in test

* Add integration test with replicas: 1

* Go nuts with the verbosity of allocation decisions

* Also check NODE_C in unit test

* Test with randomly assigned shard

* Fix test for extra verbose decision messages

* Remove canAllocate(IndexMetadat, RoutingNode, RoutingAllocation) overriding

* Spotless :|

* Implement 100% disk usage check during force-replace-allocate

* Add rudimentary documentation for "replace" shutdown type

* Use RoutingAllocation shutdown map in BalancedShardsAllocator

* Add canForceAllocateDuringReplace to AllocationDeciders & add test

* Switch from percentage to bytes in DiskThresholdDecider force check

* Enhance docs with note about rollover, creation, & shrink

* Clarify decision messages, add test for target-only allocation

* Simplify NodeReplacementAllocationDecider.replacementOngoing

* Start nodeC before nodeB in integration test

* Spotleeeessssssss! You get me every time!

* Remove outdated comment
# Conflicts:
#	x-pack/plugin/shutdown/src/test/java/org/elasticsearch/xpack/shutdown/TransportGetShutdownStatusActionTests.java