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.
unit test fix for #3052 and #3053
Added FutureUtil class to unify calls with multiple Future objects

Conflicts:
	hazelcast/src/main/java/com/hazelcast/util/ExceptionUtil.java
Merge pull request #3076 from serkan-ozal/fix/master/issue-3052-and-3053

unit test fix for #3052 and #3053
Removed some useless method overloads and lowered object allocation rate on ExceptionHandlers
Renamed test methods, fixed compile errors
fixes #3110
Merge branch 'master' of https://github.com/hazelcast/hazelcast
Improved IO threading model documentation
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.
Merge pull request #3114 from pveentjer/doc/3.x/io-threading-model

Improved IO threading model documentation
Java Client section more improvements.
Reviewed IO threading section improvements
Reviewed Java Client section authored by Asim.
Merge pull request #3107 from noctarius/github_issue_2964

Added FutureUtil class to unify calls with multiple Future objects
fix for #2676
Removed ToDos from SPI section.
unit test for #2676