Add stub ClusterInfoService, DiskUsage and DiskThresholdDecider

Change AllocationDecider API to take ClusterInfoService, update all
other deciders
flesh out DiskThresholdDecider mock a bit more
start work on ClusterInfoService
more fleshing out of DiskThresholdDecider
refactor ClusterInfoService into InternalClusterInfoService and
ClusterInfoService interface so it can be injected into BalancedShardsAllocator
missing license
use ClusterInfoService instead of InternalClusterInfoService for BSA
fail-open for no node info
Switch to threaded update, still not able to get a client node properly