This commit implements proper metadata recovery for Zen2.
GatewayService is responsible for the recovery. In Zen1 GatewayService
creates an instance of Gateway, that is used to reach out to other cluster
nodes, get their state and calculate the most up-to-date state based on
versions. After that Gateway performs upgrade and archival of
ClusterSettings and closes bad indices. Then recovered state is passed to GatewayService.GatewayRecoveryListener that mixes up current state
and restored state, removes state not recovered block, creates the
routing table and performs re-routing.
In Zen2 we should perform this kind of logic on cluster startup, except
mixing state (because there is nothing to mix) and opening routing table.
This commit refactors out all `ClusterUpdate` functions in a separate class
`ClusterStateUpdaters`, which is used by `Gateway` and `GatewayService`
in case of Zen1, and by `GatewayMetaState` and `GatewayService` in case of
Zen2.
This commit also switches all integration tests that are already using Zen2 from
InMemoryPersistedState to GatewayMetaState.
35e3d77e2c