Customisable cluster snapshot with sql and filter fun per table

[shamis]

Default cluster snapshot implementation (existing)

• Takes snapshot of the tables in the configured list [{imem,imem_snap,snapshotClusterTables}]
• Puts these snapshots a folder and zips the folder
• executes everyday at [{imem,imem_snap,snapshotClusterHourOfDay}]
• can be enabled or disabled with [{imem,imem_snap,snapshotCluster}]

New feature : support for custom cluster snapshot

• list of sqls (instead of table names). gives more control over data
• filter fun associated with each sql to filter the data after the execution of sql to remove certain rows or modify them
• configuration flag to enable and disable the custom snapshot
• configuration for cluster snapshot zip file name