Create BackedupMapDataLossTest

Test case to validate nulls being returned by a distributed map on n/w disconnections, in a cluster of 3 nodes with backup count set to 3.
Merge branch 'master' of https://github.com/hazelcast/hazelcast
Modified Set documentation to include more details on partitioning and backup storage
Deleting unwanted test case
Merge pull request #3115 from wildnez/tempo

Modified Set documentation to include more details on partitioning and backup storage.