FileSystem Quotas

Umbrella issue for tracking the filesystem utilization of HBase data, defining quotas on that utilization, and enforcement when utilization exceeds the limits of the quota.

At a high level: we can define quotas on tables and namespaces. Region size is computed by RegionServers and sent to the Master. The Master inspects the sizes of Regions, rolling up to table and namespace sizes. Defined quotas in the quota table are evaluated given the computed sizes, and, for those tables/namespaces violating the quota, RegionServers are informed to take some action to limit any further filesystem growth by that table/namespace.

Discuss: https://lists.apache.org/thread.html/66a4b0c3725b5cbdd61dd6111c43847adaeef7b7da5f4cd045df30ef@%3Cdev.hbase.apache.org%3E
Design Doc: http://home.apache.org/~elserj/hbase/FileSystemQuotasforApacheHBase.pdf or https://docs.google.com/document/d/1VtLWDkB2tpwc_zgCNPE1ulZOeecF-YA2FYSK3TSs_bw/edit?usp=sharing