Introduce a new ImmutableOpenMap
this map is a "true" immutable map, encapsulating an open impl, and has a builder that allows it to be built easily.
the builder has the optimization of using clone if its being built based on an existing immutable map.
Fixed ack behaviour when no ack is expected from any node or timeout is set to 0

We now return acknowledged true when no wait is needed (mustAck always returns false). We do wait for the master node to complete its actions though. Previously it would try to timeout and hang due to a CountDown#fastForward call when the internal counter is set to 0

We now return acknowledged false without starting the timeout thread when the timeout is set 0, as starting the wait and immediately stopping the thread seems pointless.

Added coverage for ack in ClusterServiceTests
remove unneeded check...
protect ImmutableOpenMap builder from using the built map after build has been called
Stableize recoverWhileRelocating by expanding replicas at the end
fix test to not rely on execution of processed / ack order

also, make sure the order is consistent (as much as possible) when calling ack to processed
cleanup MetaData#Builder construction
have a better method name, and only allow to create a copy of the builder based on existing meta data when constructing the builder
cleanup MetaData#Builder construction
have a better method name, and only allow to create a copy of the builder based on existing meta data when constructing the builder
cleanup RoutingTable#Builder construction
have a better method name, and only allow to create a copy of the builder based on existing routing table when constructing the builder
have IndexMetaData Builder pattern similar to other state builders
cleanup ClusterState#Builder construction
have a better method name, and only allow to create a copy of the builder based on existing cluster state when constructing the builder
cleanup DiscoveryNodes#Builder construction
have a better method name, and only allow to create a copy of the builder based on existing nodes when constructing the builder
Add missing .get() call to actually execute the update setting in RecoveryWhileUnderLoadTests
URI routing parameter does not work with Bulk API
closes #4053
URI routing parameter support with multi search API
Support URI level routing parameter for the multi search API, that will act as the default routing (unless explicitly set).
closes #4058
Resolve aliases on redirects inside TransportMoreLikeThisAction

fixes #4045